2011 nutrition and fitness

Marshall CavendishReferenceNew York

NUTRITIONAND FITNESSNUTRITION

AND FITNESS

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Marshall Cavendish

Copyright © 2011 Marshall Cavendish Corporation

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Library of Congress Cataloging-in-Publication DataNutrition and fitness.

p. cm.Includes index.ISBN 978-0-7614-7939-0 (alk. paper)

1. Health--Encyclopedias. 2. Nutrition--Encyclopedias. 3. Physicalfitness--Encyclopedias.

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This volume is not intended for use as a substitute for advice,consultation, or treatment by a licensed medical practitioner. The reader is advised that no action of a medical or therapeuticnature should be taken without consultation with a licensedmedical practitioner, including action that may seem to beindicated by the contents of this work, since individualcircumstances vary and medical standards, knowledge, andpractices change with time. The publishers, authors, and medicalconsultants disclaim all liability and cannot be held responsiblefor any problems that may arise from use of this volume.

BODY

DIET AND NUTRITION

HUMAN BEHAVIOR

ILLNESS, INJURY, AND DISORDERS

PREVENTION AND CURE

Key to color coding of the articles

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Foreword 4

Acupressure 5Acupuncture 6Aerobics 7Aging 8Alexander Technique 10Amphetamines 11Analgesics 12Anemia 13Anorexia and Bulimia 15Antioxidants 18Appetite 19Arthritis 20Asthma 23Athlete’s Foot 25Autonomic Nervous System 26Backache 28Balance 30Basal Metabolism 32Black Eye 33Blisters 34Blood Pressure 35Body Systems 36Bruises 42Calcium 43Calories 44Carbohydrates 45Celiac Disease 46Chiropractic 47Cholesterol 48Chronic Fatigue Syndrome 49Circulatory System 50Coffee and Tea 51Constipation 52Cramps 54Diabetes 55Diet 58Dieting 60Digestive System 63Digestive System

Diseases and Disorders 66Disabilities 69Drinking Water 71Elbow 72

Exercise 73Fainting 76Fats 77Feet 78Flavonoids 81Food Additives 82Food and Nutrition 84Food Labeling 91Food Poisoning 92Fractures and Dislocations 93Glands 96Growth 98Hamstring Injuries 101Health Foods 102Heart 103Heart Attack 105Heat Sickness 106Hernia 107Hip 108Homeostasis 109Hyperventilation 110Ice Therapy 111Indigestion 112Iodine 113Iron 114Irritable Bowel Syndrome 115Isometric Exercises 117Jogging 118Joint Disorders 119Joint Replacement 121Joints 123Junk Food 124Knee 125Leg 126Lethargy 128Ligaments 130Malnutrition 131Massage 133Milk 134Minerals 135Motor Neuron Disease 136Muscle 137Muscle Diseases and

Disorders 139Nervous System 141

Nosebleed 143Nutritional Diseases 144Obesity 145Orthopedics 146Osteopathy 148Oxygen 149Pain 150Paraplegia 153Physical Examination 154Physical Fitness 155Physical Therapy 160Podiatry 161Posture 162Protein 163Puberty 164Reflexes 167Respiratory System 168Rest and Relaxation 170Salmonella 172Salt 173Sciatica 174Scoliosis 175Scurvy 176Shoulder 177Skeletal System 178Skin 180Slipped Disk 182Spinal Column 183Spinal Cord 184Sports 185Sports Injuries 188Sprains and Strains 191Stroke 192Sugars 193Sunburn 194Sweat 195Tendon 196Tennis Elbow 197Tiredness 198Vegetarianism 199Vitamins 200Weight Control 204Yoga 205

Index 206

Contents


It seems as if there is nutrition and physical fitnessinformation everywhere you turn—in magazines, on

television, in newspapers, on the Internet, even onbillboards advertising full-service health clubs andclinics. Everyone has a new way for you to becomehealthier! Maintaining your wellness is more than justeating healthier and exercising. It encompasseseverything from your body and its parts to yourlifestyle choices. With so much advice available, it is hard to know what is reliable and where you can turn for accurate information.

The human body is an amazing machine. When it works well its performance is seamless, and webarely notice that we are functioning. However,when the body does not work well, we becomeconcerned. For example, we barely notice we have a shoulder until it hurts; its presence and functionare a normal part of our existence until it ceases tofunction properly. When there is a problem, we havequestions. How to maintain wellness and what thebest options are for maintaining health are importantissues for everyone to understand.

Modern life has led to new fitness and nutritionchallenges. Our relatively sedentary lifestyle and the abundance of junk food, for example, have led to complications such as obesity and its relatedproblems. Strain injuries such as those associatedwith posture in the workplace have sparked a wholenew area of study. In fact, there is probably moreresearch into health issues than anything else. When discomfort or illness strike, we look foranswers and may take curative measures before we consult a physician.

With a wide scope of more than 125 articles,Nutrition and Fitness provides enough information to answer general questions and can serve as astarting point for more in-depth study. This bookcaptures a diverse assortment of fitness and nutritiontopics: acupuncture, the circulatory system, coffeeand tea, dieting, exercise, fats, growth, isometricexercises, joints, junk food, massage, pain, physicalfitness, reflexes, sports injuries, sunburn, sweat, and yoga, just to name a few. Each article has aneasy-to-read layout, and sidebar elements highlight

important information for quick reference.As a practical, authoritative resource, thisvolume is indispensable.

In fact, the ease with which informationis available to the reader invites one tocontinue reading in topic areas that maynot be of immediate interest or necessity.Thus, the vital information in this bookserves to help the reader proactivelyaddress a variety of wellness issues.

Dr. Rashmi NemadeRashmi Nemade is a biomedical writer and editor.

Additional related information is availablein the 18-volume Encyclopedia of Health,fourth edition, and the correspondingonline Health Encyclopedia database atwww.marshallcavendishdigital.com.

Foreword

4


5

Acupressure is a Chinese healing technique that involvesapplying pressure to parts of the body to treat disease. One ofthe concepts of Chinese medicine is chi. This essential life force issaid to flow through the body along energy channels calledmeridians. Specific points, called acupoints, along the meridiansregulate the flow of chi through the body. There are hundreds of these acupoints on the human body. When a person is healthy,the flow of chi is in balance with the body and the surroundings.Disease occurs when something upsets the balance among chi,the body, and the environment. Acupressure can then be used to stimulate the acupoints. This pressure unblocks the meridiansand restores the flow of chi to treat the disease.

Acupressure is used to treat many medical conditions, whichrange from allergies and arthritis to migraines and menstrualproblems. The treatment may last for several weeks if theproblem is acute. Acupressure can also be used as a preventivemeasure. Regularly stimulating the acupoints relieves dailystresses and strains and keeps the body in balance.

A typical sessionAcupressure sessions usually take place in a quiet and relaxedenvironment. To start, the therapist will ask the patient a fewquestions and carry out a general medical checkup. The therapistthen treats the patient on a massage table or on a mat on thefloor. A typical session lasts between 30 minutes and one hour.

At the end of the session, thetherapist may suggest some self-help techniques for the individual to carry out at home.

Acupressure is widely accepted in modern medicine. Some doctorsthink that the treatment works by stimulating the production of painkilling chemicals calledendorphins in the brain. Otherdoctors think that acupressurestimulates nerve fibers to preventpain signals from traveling throughthe body to the brain.

Q & AWhat kinds of complaints reallybenefit from acupressure?

Acupressure can be a useful wayof complementing conventionalmedical treatment, especially in reducing tension, stress, andmuscle pain, but it is notrecommended as the main formof treatment for a major disease.If you experience any unusualsymptoms, such as chest pain ora severe or prolonged headache,it is always best to consult adoctor before trying acupressure.

Are there any situations whenacupressure should be avoided?

Acupressure may be harmful if a person has osteoporosis(brittle bones), a bleedingdisorder, circulatory problems,varicose veins, or carpal tunnelsyndrome (which is caused bypressure on a nerve). In addition,pressure should not be appliedto wounds or inflamed skin.People taking steroids are also at risk, because the drugs maketheir tissues fragile.

Acupressure

Some therapists believe that usingacupressure around the facial area may help reduce wrinkles and improve the appearance of the skin.

SEE ALSOacupuncture • massage • muscle • nervous system • pain

• rest and relaxation • skin • tiredness

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6

Acupuncture is an ancient healing art that has been used in China for 5,000 years. Now, people in other countries are using this treatment. Acupuncture is based on the belief thatenergies flow through channels under the skin. When an organ is diseased, the flow of energy is disturbed. Acupuncturists work from a map of the body showing key points along thesechannels. They believe that they can correct a disturbance byplacing very fine needles in the body at one or more points.

Acupuncture certainly seems to help many people, particularlythose with arthritis, headaches, digestive problems, asthma, andhypertension. Modern scientists think it either stimulates thebody to produce painkilling hormones or triggers pain-blockingmechanisms in the nerve pathways. The treatment is often usedto relieve pain and can even be used instead of an anesthetic in some surgical operations and during childbirth. The patientremains conscious but does not experience any pain.

Q & AI’ve seen pictures of people withacupuncture needles in them. Is that as painful as it looks?

There may be a slight, brief prickas the needle enters the skin. As the treatment starts to takeeffect, people usually feel onlynumbness, or sometimes a slightaching, or tingling.

Do the needles make you bleed?

Usually not, because the smooth,fine, supple acupuncture needlesdo not damage tissues. Points on the face and ear bleedoccasionally because the skinthere has a rich blood supply.

How long does it take for thetreatment to work?

Acute complaints may improveimmediately or within a week or two. Chronic conditions maytake perhaps two or threemonths of weekly treatments,although some benefit should be noticed within a few weeks.

Acupuncture

Acupuncture needles have an anestheticeffect powerful enough to allow surgeryto take place while the patient is fullyconscious. This woman appears perfectlyrelaxed as needles are inserted in her face.

acupressure • analgesics • massage • nervous system

SEE ALSO


7

An aerobic exercise is one in which the muscles, lungs, and heartwork hard enough to make a person feel breathless and sweaty.Many types of exercise, including cycling, brisk walking, jogging,and swimming, are aerobic. This sort of exercise helps peoplekeep fit. Aerobic exercise forms part of an athlete’s training, andmany people who want to improve their general health go toaerobic exercise or dance classes.

Regular aerobic exercise improves the way the body utilizesoxygen. It increases the amount of air that reaches the lungs, sothat more oxygen is carried by the blood to the muscles. It alsomakes the heart muscle pump the blood around the body moreefficiently. Underdeveloped blood vessels are opened, and newcapillaries (tiny blood vessels) develop in the muscles.

Aerobic exercise should be performed for about 20 minutes at least three times a week. As people exercise, their fitnessincreases. This can be shown by recording the heartbeat after the first exercise session; it will be quite fast. As the bodybecomes more efficient, it will be able to carry out the same

program without raisingthe heartbeat nearly somuch. However, peopleshould be careful to buildup their exercise programcarefully and steadily.They should not tirethemselves out byexercising too hard atfirst. It is best to do about10 minutes of warm-upexercises before eachsession and some cool-down exercises afterward.

Aerobic exercise classesare popular and can behelpful, but they shouldbe taught by qualifiedinstructors. People caneasily injure themselves if they exercise too hardor in the wrong way.

Q & AAre people right when they saythat aerobics requires a “no pain,no gain” attitude?

You should never set out tocause yourself physical harm.Listen to your body. If you feelany sudden pain, slow your paceuntil you come to a gentle stop.If the pain is severe, stop at once.

Will running at four miles anhour for 10 minutes give me the same aerobic benefits asrunning faster over the samedistance in less time?

Endurance time is moreimportant than speed. You will gain greater benefit fromrunning for 10 minutes at a slowpace, because your pulse ratewill be sustained for longer.

I took up aerobics to lose weight,but I’ve gained weight. Why?

You may be losing fat, but yourmuscles will increase in densityas they gain tone.

Aerobics

This man is on a treadmill. He is beingmonitored to find out how much oxygenhe takes in during exercise. This test isoften carried out to check an athlete’sperformance during training.

exercise • heart • muscle • oxygen • sports injuries

SEE ALSO


8

As people grow older, some parts of the body change andbecome less efficient and even begin to deteriorate. Old skinbecomes much less elastic than young skin, for example, andtends to become dry and wrinkled. Hair turns gray, some people’ssight may not be good, and many people may become hard ofhearing. The heart, bones, and muscles are less strong. Mostpeople even grow smaller as they get older, because the padsbetween the vertebrae shrink. These changes happen becausethe body’s cells are wearing out and the production of new cellsdecreases as people get older.

Staying healthy and activeSome people stay young-looking and active far longer thanothers. This is partly because of the genes that they haveinherited. People who come from long-lived families are morelikely to live a long time themselves, and some people may alsoinherit genes for healthy and long-lasting eyes, memory, heart,and so on. However, everyone can increase the chances of ahealthy and active old age by keeping fit and healthy whenyoung. Regular exercise as people get older helps keep them fit, supple, and active into old age. Exercise also often improves

Q & AMy father is a heavy smoker. Willsmoking affect his longevity?

Yes, it will. Many peopleunderestimate the risk they aretaking by smoking 25 cigarettesa day (even low-tar brands).Smoking will almost alwaysspeed the aging process; it cancause death from heart diseaseand diseases of the lungs andarteries before the age of 60. It affects the skin; people whosmoke heavily often wrinkleprematurely. Smoking is not just a minor hazard; it is a majorcause of premature death.

My grandmother has shrunkover the past two years. Why?

Height loss is mainly due tothinning of the spinal bones andshrinkage of the disks betweenthe bones. An elderly person’sback tends to bow, making himor her bend forward. Maintainingcorrect posture in earlier lifehelps to strengthen the back and may reduce later height loss.

Aging

A lifetime of healthy exercise has kept thisolder man fit enough to play competitivetennis. However, it is never too late forelderly people to start improving theirfitness levels with gentle activities.


9

the mental attitude toward aging and helps ward off thedepression that many older people experience, especially if theylive alone. Older people who keep their brains active by reading,studying, and taking an interest in other people and theirenvironment are more likely to stay alert. There are many ways in which elderly people can be encouraged to take an active partin family and community life and to play an important andhelpful role. Making elderly people feel useful and wanted is the best way to help them stay young.

Life expectancyNearly 12 percent of U.S. citizens are over 65. Because of betterhealth facilities and medical technology, people are living longerthan ever before. If a man now lives to 65, he can expect to liveanother 13 years, and he can expect another nine if he passes theage of 75. A woman of 65 will live 18 more years on average, and a woman of 75 will live 12 more years. By the year 2030, it isestimated that there will be more than 55 million Americans over 65; a great many of them will be women over 85.

Aging

People can have just as much fun whenthey are old as when they were young.Those who are active and eat a healthydiet can risk an occasional fast-food treat.

exercise • heart • muscle • physical fitness

SEE ALSO


10

The Alexander technique is not so much a therapy as a process of reeducation. It aims to treat and prevent a wide range ofdisorders by teaching people to become aware of how they usetheir body and to make the changes that they find necessary inorder to feel some physical or psychological benefit.

The conditions that have been found to respond best to theAlexander technique include back pain, breathing difficulties,neck and joint pain, and stress-related disorders such asheadaches and fatigue. It has also been found helpful in suchdiverse conditions as high blood pressure, spastic colon, asthma,osteoarthritis, and neuralgia.

The Alexander technique is often referred to as posturetraining but this is not strictly correct, though improved posturedoes often result from its use. The technique aims to get peopleto use their body in a relaxed, balanced, and efficient way withnatural ease and grace.

Traditionally, the technique is taught on a one-to-one basisand usually requires about 30 lessons at weekly intervals. Eachlesson lasts about 30 to 40 minutes, during which time theteacher helps the student look in great detail at the way in whichhe or she uses the body. Students are taught to look at theirpersonal tension patterns while they are engaged in a range of different activities, which usually include sitting, standing, or walking. They will probably also work lying down on a table.The teacher uses his or her hands, accompanied by verbalinstructions, to direct the student to release tension.

How it worksThe Alexander technique was developed by an Australian actor,Frederick Matthias Alexander (1869–1955), who believed that“every man, woman, and child holds the possibility of physicalperfection; it rests with each of us to attain it by personalunderstanding and effort.” The Alexander technique works onthe principle that mind and body form a whole. Although thatproposition is now widely accepted, it was considered radicalwhen Alexander came up with his technique at the turn of the twentieth century. The technique does not treat specificconditions, but rather aims to address the source of a problem. In restoring harmony of both mind and body to a person, it isfound that many specific problems disappear.

Q & AWill the Alexander techniquehelp me lose weight?

No, it is unlikely. However, byimproving your posture andlearning how to stand upright,you may look taller and give theimpression of being slimmer.

Sometimes I get bored,depressed, and tired for noreason. Could the Alexandertechnique help me?

If you have no specific illness orphysical disorder, it may simplybe that your system is notworking properly; this can leadto low spirits and fatigue. Byteaching you to listen to yourbody and to release any tensionyou are holding, the Alexandertechnique can restore yourenergy levels and general stateof well-being.

Do I have to be good at sports to be any good at the Alexandertechnique?

The Alexander technique is not a physical test; it is a gentle,natural method that works withthe body and that can be learnedat almost any age, whether youare fit or unfit.

AlexanderTechnique

asthma • backache • blood pressure • joints • posture

SEE ALSO


11

Amphetamines are powerful, habit-forming stimulant drugs thatare chemically related to the body’s own stimulant, adrenaline.Taking amphetamines increases mental alertness and physicalstamina, relieves depression, and aids dieting by suppressing the appetite. However, the long-term effects are harmful.

Amphetamines were once widely used until they were found to be habit-forming. People who took them over a period of time needed larger and larger doses to get the effect theywanted. Some people who depended on them becameaggressive and violent. Others became listless and depressed.Still other people had mental breakdowns with delusions andhallucinations. As a result, doctors are now understandablyextremely wary of prescribing amphetamines. These drugs now have few uses in medicine and are seldom prescribed for any purpose.

Children with attention deficit disorders and hyperactivity are no longer given prescribed amphetamines, although theymay be given amphetamine-related stimulant drugs, such asmethylphenidate (Ritalin).

Amphetamine abuseIn the 1960s, amphetamine abuse was common. Drugs known as “purple hearts” and “black beauties” were taken by people who wanted a quick high and by students who wanted to stayalert to study for long hours. “Speed freaks” injected themselveswith amphetamine solutions. Inhalers containing the drug wereavailable over the counter.

One of the most popular stimulant drugs is the amphetaminederivative ecstasy. The side effects of ecstasy include loss ofappetite, irritability, fast talking, abnormal extroverted behavior,fast pulse, heart irregularities, paranoia, hallucinations,depression, bleeding in the brain, and possibly damage to the liver. Extreme and excessive physical activity is commonlybrought on by the high produced by ecstasy.

Amphetamine abuse is now less common. People who havebecome dependent on amphetamines require medical help. Theymay have a mental breakdown, which results in delusions andhallucinations. Some symptoms of amphetamine abuse aresimilar to those of schizophrenia, an acute personality disorderthat requires hospitalization.

Q & AI love bicycle racing and want toturn professional in the future.Would taking amphetaminesbefore races improve my stamina?

It is not safe to use these drugs.After several professional cycliststaking part in the Tour de Francerace died as a result of usingamphetamines, national andinternational sports agenciesbanned the use of stimulants. If you took amphetamines, youwould be not only seriouslyendangering your health butputting your professional careerat risk as well.

My little brother seems to needless sleep than the rest of ourfamily. He’s still jumping aroundat two in the morning. Can myparents just give him some pillsto calm him down so we can allget some sleep?

No. Your parents should getsome professional advice. Yourdoctor will advise them whetheryour brother is really hyperactiveor just needs very little sleep.Never give a child pills withoutmedical advice. A dose that hasbeen prescribed for adults will betoo strong for a child and will domore harm than good.

Amphetamines

appetite • dieting • heart • tiredness • weight control

SEE ALSO


12

Q & AI saw my father drinking analcoholic beverage even thoughhe is taking an analgesic. Is thata safe thing to do?

If your father is using a mildanalgesic such as aspirin, anoccasional drink should be safefor him. However, both aspirinand hard liquor can causebleeding in the gut, so it is wiseto avoid the combination.Alcohol should never be taken at the same time as a strongpainkiller, because bothsubstances slow breathing and the interaction of the twosubstances could be dangerous.

I get migraines, but if I don’ttake a painkiller as soon as anattack starts, the pill doesn’twork. Why?

When a migraine attack occurs,the functioning of the intestine,which is controlled by thenervous system, shuts down.Once this happens, there is little chance of a drug’s beingabsorbed in the gut. If you areunable to take a pill as soon asan attack starts, your doctor may prescribe an analgesic insuppository form or an oral drug that will help absorption.

Analgesics

circulatory system • heart attack • pain • stroke

SEE ALSO

Prostaglandins cause theblood vessels to widen andleak fluid. White cells moveinto the tissue, whichbecomes red and swollen.

NSAIDs limit the release ofprostaglandins. The bloodvessels return to normal,and swelling and rednessdecrease.

Analgesics are drugs that relieve pain. Some analgesics, includingaspirin (acetylsalicylic acid), acetaminophen, and ibuprofen, are mild and can be bought without a prescription. Aspirin andibuprofen are two examples of a class of painkilling drugs callednonsteroidal anti-inflammatory drugs (NSAIDs).

Aspirin is the most commonly used analgesic drug in theworld. It reduces inflammation and fever and is used mostly for minor ailments such as headaches and in the treatment ofrheumatic diseases. People may be more likely to survive heartattacks and strokes if they are treated with aspirin and less likelyto have those diseases if they take a small daily dose of aspirin.

Aspirin counteracts the effects of prostaglandins (fatty acids,made naturally in the body, that act like hormones). However,large amounts of aspirin can cause intestinal bleeding in adults.A link has also been discovered between aspirin and Reye’ssyndrome, a rare but very serious condition in children. Aspirinshould not be given to children under the age of 12, except withmedical supervision. Ibuprofen is a more powerful painkiller andalso causes less stomach irritation than aspirin.

Other analgesics have a very strong effect and can be boughtonly with a doctor’s prescription. They include drugs, such ascodeine and morphine, that can be habit-forming if taken over a long period.

prostaglandin

white blood cell

analgesic


13

Anemia is a disorder that is caused by an abnormally low level ofhemoglobin in the blood. It occurs when the number of red bloodcells that contain hemoglobin is low or when the cells containlow levels of hemoglobin.

Hemoglobin picks up oxygen in the lungs and carries it to the body tissues, where it provides energy. If the hemoglobin in the blood falls below normal levels, too little oxygen reachesthe tissues. That produces the classic symptoms of anemia: skin pallor, breathlessness, and lack of energy. These symptomsmay be accompanied by palpitations (rapid and noticeableheartbeats), fainting, dizziness, and sweating.

Types of anemiasA common cause of anemia is a lack of iron, which is an essentialcomponent of hemoglobin. Women are particularly likely toexperience this deficiency, because of the amount of blood theylose each month in menstruation, especially if they have veryheavy periods. Other causes include ulcers that produce slow but steady internal bleeding, cancer of the stomach or intestine,hemorrhoids, and parasites such as hookworms and tapewormsthat feed on the blood. Thirst is a symptom of iron-deficiencyanemia; anemic children may be irritable and have a tendency to hold their breath.

Without vitamin B12 and folic acid, fewer red blood cells can be made, and those that are produced are enlarged. In the UnitedStates, people’s diets usually contain plenty of B12, but in somepeople, the stomach lining fails to produce a substance known as intrinsic factor. Without this factor, B12 cannot be absorbed,and red blood cell production falls. This condition is known aspernicious anemia. It can cause tingling sensations in the handsand feet, nosebleeds, and, in severe cases, heart failure and nervedamage, as well as the usual symptoms of anemia.

Folic acid deficiencyFolic acid is usually supplied by green vegetables in the diet. Adeficiency of folic acid generally occurs in elderly people who arenot eating properly, in pregnant women who use extra folic acidto nourish the developing baby, and in people who drink excessamounts of alcohol. These anemias can be treated by increasingsupplies of the deficient substance. Iron tablets or shots rectifydeficiency anemia in a few weeks. Folic acid deficiency can betreated with tablets and an adequate diet.

Q & AMy mother is pregnant and isgetting paler and paler. Couldshe be anemic?

During pregnancy, the body’sdemand for essential nutrients,such as iron and folic acid, isincreased. The developing fetusdepletes the mother’s store ofnutrients via the placenta, andthe mother may then becomedeficient in one or more of them,causing anemia, unless extrairon and folate are given. Yourmother should check with herdoctor, who will give her aprescription for supplements if they are necessary.

Anemia

Green leafy vegetables such as salad leaves and spinach are an importantsource of folic acid and iron, a lack of which can cause anemia.


14

Red blood cells play an important part in anemia. (1) When there are enoughchemicals to produce the requirednumber of blood cells, the cells carryadequate oxygen supplies around thebody to give energy. (2) When there arenot enough chemicals to produce thenumber of red blood cells required, lessoxygen reaches the tissues, resulting intiredness. (3) Sometimes there are enoughchemicals, but a number of red blood cells are malformed. They may block small arteries and cause severe pain and disability.

Vitamin B12 and pernicious anemiaIf the stomach lining has ceased to produce intrinsic factor, it willnever be able to absorb vitamin B12. Regular shots of vitamin B12for the rest of the patient’s life will keep pernicious anemia undercontrol, although it will recur if shots are missed.

Hereditary anemiasSometimes, red blood cells are destroyed more quickly than they can be replaced, causing hemolytic anemia. Two serioustypes of hemolytic anemias are hereditary. Sickle-cell anemia is present largely in black communities. Thalassemia is present in Mediterranean, Middle Eastern, and Southeast Asiancommunities. Both types of hereditary anemia are serious andincurable, but they can be helped with blood transfusions.

Anemia

2 LACK OF ENERGY

3 PAIN AND DISABILITY

1 ENERGY

diet • iron • oxygen • pain • vitamins

SEE ALSO


15

Anorexia, or anorexia nervosa, is a compulsive desire to loseweight, which goes far beyond any ordinary wish to become thin.Left untreated, it can be fatal. It usually affects young peoplebetween the ages of 11 and 30 and occurs more often in girlsthan in boys. Anorexia nervosa used to be rare, but it is becomingincreasingly common, particularly in people from middle-classhomes. This is a serious disorder of perception in which thesufferer—a girl, for example—is convinced she is too fat when, infact, she may be desperately thin. The affected girl may also befrightened of her developing sexuality and feel that if she cankeep her childish figure, then she will not have to face up to theproblems of adult sexuality. The danger of anorexia must neverbe underestimated; skilled management by experts is required.Up to 20 percent of cases end fatally.

Some emotionally insecure girls and boys diet drastically to increase their sexual confidence. The idea that being thin is a desirable state is reinforced constantly by television andmagazine advertizing that promotes thinness by glamorizingunnaturally thin supermodels.

Addicted to dietingNormal people who diet drastically can usually stop wheneverthey choose, perhaps when they have reached their targetweight. Their problem is usually to keep to a diet when there isfood around them, since hunger is such an unpleasant sensation. Anorexics, once started, cannot go into reverse. They are asaddicted to dieting as if they were taking drugs. They may even experience some of the same light-headedness.

Anorexics go to great lengths to hide what they are doing.They may be unusually energetic and insist that they are well.They cook large meals for other people, while eating nothingthemselves. They tell lies, saying that they have eaten elsewhere,and become very skilled at hiding food while pretending to eatnormally. Some make themselves vomit to get rid of food theyhave been coaxed to eat, or they use laxatives, diuretics, and evenenemas to prevent their bodies from absorbing nourishment.Some anorexics develop a binge-and-vomit pattern calledbulimia. They eat large quantities and then make themselvesvomit so that they can eat without putting on weight.

Symptoms of anorexia nervosaThe first, obvious symptom of anorexia nervosa is continued loss of weight. It may not be easy for the anorexic’s family to recognize the symptom until it has become severe. Anunmistakable symptom in a girl is that once her weight has

Anorexia and Bulimia

Q & AMy friend has been told she is anorexic but doesn’tbelieve it. Why can’t she realize how emaciated she looks?

She is suffering from anabnormal mental state. Whenshe looks in a mirror she sees a distorted body image thatinitiates, and prolongs, thedisease. Your friend should get help from a counselor or doctor.

Sometimes I eat a bag ofcookies. Then I’m sorry, so I make myself vomit afterward.Am I suffering from bulimia?

Not unless these binges havebecome uncontrollable andfrequent. Many dieters go on an eating binge after theyhave been on a strict diet forsome time. A binge is not good for the body, but it does no lasting harm. Only when it becomes a way of life should you seek treatment.You seem to feel guilty aboutovereating, but try to beless emotional about it andattempt to lose weight in a more sensible way.


16

fallen more than around 26 pounds (12 kg) below normal, shestops menstruating. Girls or boys who diet excessively and seemto have a false image of being overweight should be seen by aphysician as soon as possible. They may simply need advice andinformation on the weight they should try to achieve and on a proper diet. However, if they have anorexia nervosa, it isimportant to begin treatment as soon as possible. The longer the condition goes untreated, the more difficult it is to cure.

Perhaps one in five anorexics eventually dies of starvation or from infections caused by undernourishment. Some become so depressed that they commit suicide. Cures seldom take placewithout treatment, because victims take pride in their condition.The more distorted their self-image, the more difficult the cure.

Treating anorexia nervosaThe first step is to increase body weight, at least above thedanger level. Research indicates that when a patient is below acertain weight, psychotherapy cannot break through the strangemental isolation caused by voluntary starvation. Until a morenormal weight is reached, no real communication can take place.

It is usually better to treat anorexics at a hospital. Their foodintake must be checked carefully because they tend to hide orthrow away food to avoid eating. There is also the possibility that they will fake their weight gain by putting weights in their pockets before they step on scales. This behavior can bemonitored more easily in a hospital. Sometimes, patients aremade to rest in bed, very often in a room alone, and their foodintake is strictly monitored by the nursing staff. In the earlyphases of treatment, patients may also be given a form oftranquilizer and be fed intravenously. Sometimes, a system ofrewards and withdrawal of privileges is used to coax the patientto eat normal food and gain a certain amount of weight.

Once the patient has gained enough weight to be out ofdanger, psychotherapy can begin. This approach may be requiredfor months or years after the patient is at normal weight. Often,the whole family is given counseling, so that the parents canunderstand the nature of their child’s illness and what causes it.

BulimiaBulimia is another eating disorder. It may appear on its own, butit often goes with anorexia nervosa. Its severe form is calledbulimia nervosa. This condition is most often present in girls andyoung women who become convinced that they are overweight,although in most cases, their weight fluctuates between a littleabove and a little below normal.

Before and after: This 19-year-old anorexicgirl needed hospital treatment. After twomonths she had a normal body weight.


The longer the illness lasts and the more weight the anorexicloses, the greater is her sense ofachievement. She believes thatbeing thin makes her significantand outstanding as an individual.Her behavior focuses attention onherself and sometimes gives her asatisfying form of rebellion againstthe authority of her parents.

EMACIATION AS A SENSEOF ACHIEVEMENT


17


People with bulimia eat very large meals, or binge. The fear of becoming overweight then prompts self-induced vomiting.They tend to eat in secret and are unable to control themselves.During binges, they may eat up to 12,000 calories in just a fewhours. These binges are often triggered by stress and may takeplace several times a week or several times a day. The patientmay not eat at all between binges. Bulimics do not usuallybecome seriously underweight, as anorexics do, but they cancause themselves physical harm by overloading their systemswith food and through the subsequent taking of laxatives. Theysuffer from weakness and cramps, as well as dehydration, andtheir teeth may become damaged by gastric acid. Treating theirunderlying psychological problems often helps the condition.

People with anorexia nervosa have anoverwhelming desire to lose weight andconstantly weigh themselves to ensurethat they have not gained any.

Many teenagers with anorexia nervosaenjoy cooking for other people, but theyare reluctant to eat the food themselves,even if they are hungry.

diet • dieting • malnutrition • weight control

SEE ALSO


18

Antioxidants are substances that mop up some of the harmfulby-products of metabolism and prevent the damage caused by outside factors such as cigarette smoke and ultraviolet radiation from the sun.

The body needs oxygen to utilize food in a process calledmetabolism. Hundreds of thousands of chemical reactions occurduring metabolism. Some by-products of these reactions arechemicals called free radicals. Free radicals are also producedwhen the body is exposed to infections and environmentalfactors, including ultraviolet radiation from sunlight andpollution such as cigarette smoke. Free radicals attack the cellsand tissues of the body and contribute to the effects of agingand major health problems such as cancer and heart disease.

Double defenseThe body has two mechanisms to cope with free radicals. Thefirst line of defense involves substances called antioxidants. Theydestroy free radicals and prevent them from damaging the body.Antioxidants include vitamins C and E and substances calledcarotenoids (which are present in a wide range of foods) andflavonoids (from sources such as tea and grape skins). The secondline of defense involves enzymes that destroy free radicals andrepair the damage done to the body’s DNA (deoxyribonucleicacid), cell membranes, lipids (fats), and proteins.

Preventing diseaseMany medical experts think that by eating more foods rich inantioxidants, such as fresh fruits and vegetables, a person canreduce the risk of certain diseases. Some medical studies havealso shown that people can help prevent the onset of certaincancers by taking antioxidant supplements, such as vitamins Cand E and carotenoids. The exact benefits of taking these

supplements are still uncertain, so most health organizationssuggest eating foods that arenaturally rich in oxidants. The typicalrecommendation now is to eat at least five portions of fruit andvegetables every day.

Antioxidants

SEE ALSO

basal metabolism • food and

nutrition • vitamins

Antioxidants such as vitamin C, vitamin E,and beta-carotene are present in a widerange of fresh fruits and vegetables.

Q & AWhen did medical sciencebecome aware of free radicalsand the role of antioxidants in combating them?

Research began to emerge in the 1970s about free radicalsthat damage the body’s cells andtissues. American chemist andNobel Prize winner Linus Pauling(1901–1994) proposed thatpeople who took large, regulardaily doses of the antioxidantvitamin C had a striking decreasein the number and severity ofcolds they caught. Many peopledismissed his claims, but interestin antioxidants continued to grow.


1919

Appetite is the desire for food. It is not the same as hunger,which is the need for food. If you want to eat something becauseit looks and smells good, your appetite is working. When youwant to eat something because your stomach feels empty and you feel you really need food, you are hungry.

Appetite regulates how much someone eats and varies greatlyfrom person to person. Some people have a large appetite; theywant a great deal of food. Others have a small appetite and eatonly a little. The appetite is controlled by an area in the braincalled the appestat, which receives signals from the body andtells a person when he or she has had enough to eat. If thissystem worked perfectly, people would eat just the right amountfor the body’s needs and no more, ensuring that they had ahealthy, balanced diet. However, all sorts of things can affect the appetite. People who are overweight usually eat far morethan they need, and underweight people may feel satisfiedbefore they have had enough nourishment. Habit plays a largepart. The body can become accustomed to four or only twomeals a day rather than three.

When people become ill, they often lose their appetite.However, this may be just the time when they need to eatproperly. Pregnant women sometimes have an urge to eatstrange things or odd combinations of food, such as pickles andice cream. Emotional problems and stress can sometimes makepeople lose their appetite altogether, or might have the oppositeeffect and make them eat for comfort. As yet, scientists do notreally know the reasons why appetite varies so much.

Appetite

The color of food is important instimulating appetite. The same omelette and french fries colored blue and green look most unappealingand would probably be eaten only by a person overwhelmed with hunger.

FACTORS AFFECTINGAPPETITE

Food that looks and smells goodtempts the appetite andencourages us to eat more. So doesfood we know we like. Appetite is also affected by eating habits.People from families who enjoyeating meals together will probablyhave a larger appetite than thosewho eat alone. People can traintheir appetite to some extent bydeveloping sensible eating habits.

diet • dieting • food and nutrition • weight control

SEE ALSO


20

Arthritis is inflammation of the joints. It ranges from briefdiscomfort to severe, long-lasting pain and serious disablement.Arthritis occurs in people of all ages and can affect one joint or several. In many cases, no one knows for sure what causesarthritis. There are two main kinds of arthritis: osteoarthritis and rheumatoid arthritis.

OsteoarthritisOsteoarthritis happens as part of the aging process, and almostevery adult has some signs of it. It is caused by degeneration ofthe cartilage, which is the strong, elastic tissue that protects thesurface of the joints. The cartilage becomes rough and cracked,compressing the underlying bone and inflaming the tissue liningabove it. Osteoarthritis mainly affects the hands and the weight-bearing joints of the hips, knees, and spine. The first symptomsare pain and loss of use of the affected area, followed by stiffnessand swelling. In time, the affected joints become distorted.Osteoarthritis gets gradually worse and can be disabling if it occurs in a weight-bearing joint and is severe.

Rheumatoid arthritisRheumatoid arthritis is an autoimmune illness in which thebody’s immune (defense) system works incorrectly, producingantibodies that react against the tissue lining of the joints,causing inflammation, tenderness, pain with movement, andstiffness. This form of arthritis may be triggered by an illness,emotional stress, or shock, which causes a chain of biochemicalreactions in the body. Rheumatoid arthritis usually affects adultsbetween the ages of 20 and 55. Rheumatoid arthritis may appearsuddenly, starting with a fever or rash, or develop over severalweeks. A common symptom is inflammation of the knuckles and toe joints, and the patient may lose weight, becomelethargic, and feel generally unwell. The knees, hips, shoulders,wrists, elbows, ankles, and bones of the neck may also beaffected. The patient may have great difficulty in moving aroundand may have to stay in bed. It may be several months before theinflammation dies down, and further attacks can occur. The jointsmay become deformed and the bones around them weakened.

Still’s diseaseWhen rheumatoid arthritis occurs in children, it is known asStill’s disease. This condition is fortunately rare. It mainly affectschildren between the ages of one and three, or between 10 and15, and the child may have several attacks over the years, endingwith the onset of puberty. Each attack may last for several weeks.

Arthritis

Is it safe for my father to take a lot of aspirin to ease the paincaused by arthritis?

Yes and no. Because aspirinreduces inflammation andtemperature and eases pain, it is often used as a first-linetreatment for arthritis. However,when aspirin is taken for a longtime, there are two possible side effects: tiny gastric ulcerscan bleed or an existing ulcercan flare up.

My grandmother always wears a bandage wound tightly aroundher arthritic knee. Is this reallyhelpful?

It can be of some help.Bandaging or supporting anacutely inflamed joint can stop jarring movement and,therefore, ease some of the pain.When a joint is swollen, thetissues feel stretched. A supportunder these circumstances givesa sensation of stability. However,she should always be careful not to make the bandage too tight, because a very tight bandage can reduce the circulation of blood to the lower part of the leg.

Q & A


21

Arthritis

The child may have a rash and a temperature that rises fromnormal in the morning to about 103°F (39.4°C) in the evening;other symptoms can include swollen glands in the neck and armpits, and painful, red eyes. Eye inflammation in Still’sdisease is serious because it can permanently damage the vision; it requires skilled ophthalmic care.

Other forms of arthritisArthritis can be caused by infections, including tuberculosis,rheumatic fever, gonorrhea, and psoriasis. Once the infection is cured, the arthritis disappears. However, it can be triggered at a later date by an injury, such as a blow to a joint. Bacteria in the joint fluid can cause a damaging and dangerous septicform of arthritis. Another type of arthritis that affects the spineand pelvic joints is ankylosing spondylitis.

Many cases of arthritis are treated with drugs such as aspirinand ibuprofen, which help combat inflammation and ease thepain. Steroid drugs such as cortisone can also help the conditionbut they may have unpleasant side effects. Regular, sensibleexercise helps prevent stiffness and loss of movement in thejoints and helps muscles keep their strength. Heat treatment can ease painful joints, and swimming in a warm pool is alsogood exercise for people with arthritis.

A normal knee (below left) comparedwith an osteoarthritic knee. The smoothcartilage that cushions the joint hasdegenerated and worn away, leaving the bones to grind against each other. As the bone seeks to heal itself, its surface becomes rough and painful.

femur

kneecap

NORMAL KNEE OSTEOARTHRITIC KNEE

cartilage


22

Relieving the strain of arthritisClaims are made that special diets ease arthritis, but there is asyet no real proof of this. Too much weight puts unnecessarystrain on the joints, so heavy people with arthritis should reducetheir weight by eating sensibly and exercising. Operations toreplace the hip, the knee, and other joints damaged by arthritisare now common. The damaged joint is replaced by an artificialone made of metal or metal and plastic. This operation is usuallysuccessful and gives the patient increased movement and relieffrom pain. Surgery can also relieve pressure around a joint, canfree ligaments that have become stuck together, or can removeinflamed tissue lining a joint if it is greatly affected.

Arthritis

Fine movements with the hands are often difficult and painful for someonesuffering from arthritis. People withrheumatoid arthritis need to keep their hands as mobile as possible, but movements may be painful anddifficult to make. Sometimes, a joint(inset) becomes so deformed that it cannot be used.

aging • joint replacement • joints • pain • puberty

SEE ALSO


23

Asthma is a common condition that involves considerabledifficulty in breathing. During an attack, asthmatics tend tobreathe in with short gasps and force their breath out again with a long wheeze. Asthma is caused by a narrowing of thebronchial tubes when the muscles that line them contract. These tubes lead from the windpipe (trachea) to the lungs.

Asthma attacks are quite common in children, but mostpeople outgrow them in adolescence. Some attacks are mild but others can be extremely bad. Asthma is brought on by a number of different causes, from breathing polluted air toemotional stress. All the different causes of asthma result in the release of one of two chemicals in the body. Thesechemicals are histamine and acetylcholine, both of which cause the bronchial muscles to contract.

Histamine release is the most common cause of asthma. It is triggered by an allergic reaction to all sorts of substances,including the following: pollen; house dust; certain foods, such as shellfish, eggs, chocolate, and milk; and some preservatives.Sudden strenuous exercise and emotional upsets also causeattacks or make them worse, and the more anxious the patientbecomes, the worse the attack gets.

Most asthmatics are prescribed a bronchodilator, which theycan use if they have an attack. The bronchodilator contains asubstance that opens the bronchial tubes. People with asthmashould always carry their inhaler with them, in case they have an attack when they are away from home.

Asthma

Easy to use and convenient to carry in a pocket, this type of aerosol inhalerrelaxes and widens the airways in all but the worst asthma attacks.

What can I do if I forget myinhaler and then suffer anasthma attack?

If you suffer a severe attack, you must go to a doctor or to a hospital emergency roomimmediately. Otherwise, try to sit still and save your breath.

My father had asthma, and my sister and I now have it. Can asthma run in families?

Asthma does tend to be inherited,especially those types of asthmathat are a strong response to anallergy. However, the inheritedlink is not yet fully understood.

My young brother is asthmatic.Should he play sports?

Yes, all asthmatic children shouldbe encouraged to exercise. Somesports are more likely to causeasthma than others; swimmingis the least likely to bring on anattack. Your brother should usehis inhaler before taking part.

Q & A


24

Treatment of asthmaPeople with asthma should regularly monitor the state of theirbronchial tubes with a peak flow meter, which is prescribed bydoctors and is available in large drug stores. This simple devicemeasures the ease with which air can enter and leave the lungsand gives warning of the probability of a dangerous asthmaattack. Asthmatics can take inhaled steroids to prevent attacks or help cope with minor ones. These steroids now play animportant part in the control of asthma and can reduce thelikelihood of permanent lung damage. More severe attacks needprompt treatment from a doctor or sometimes hospitalization.If a severe attack is not treated quickly, the patient may even die.

A doctor can inject a drug such as aminophylline, which relaxesthe bronchial muscles andtakes effect immediately.Hydrocortisone injections also relieve an attack veryquickly. Asthmatics shouldhave tests to find the cause of their attacks. Regular,steady exercise, particularlyswimming, helps sufferers,but they must be careful notto overdo it. There is no curefor asthma, but currentresearch may lead to one.

Asthma

This is a photograph of a house dust mite,viewed from below and magnified manytimes. These mites are about 0.12 inch (3 mm) long and can be seen only with a magnifying glass. They are found in dust and bedding in even the cleanesthome and can trigger an asthma attack.

FIRST AID FOR ASTHMAWhen a person with asthma has a bad attack, give any drug that the doctor has prescribed andmake a note of the exact time. Sit the patient up, leaning slightlyforward (resting on the elbows canhelp). Make sure that he or she canget plenty of fresh air. Give moremedication after 30 minutes if thedoctor has said that this will be allright. If the attack does not seemto be getting better, telephone thedoctor and get ready to take thepatient to a hospital if necessary.

PREVENTING ASTHMA ATTACKS

exercise • hyperventilation • respiratory system

SEE ALSO

Cause How to prevent

Infections such as common cold and other viruses, sinusitis, Avoid people with colds, eat a balanced diet, get bronchitis enough sleep and exercise.

Allergic reaction to pollen, house dust, fungal spores, Keep home as dust-free as possible. Do not sit on carpetsanimal hair or rugs. Use foam pillows. Avoid animals. Use air cleaners.

Irritants breathed in, such as gasoline fumes, cigarette smoke, Avoid fumes and smoky atmospheres. Avoid going outfresh paint, bad odors, cold air in cold air.

Exercise or unusual physical exertion Avoid strenuous exercise. Use gentle relaxation techniques.

Sudden changes of temperature or air pressure Avoid sudden temperature changes.

Emotional upset and stress Identify cause of problem or stress and seek help for it.

Food allergies to milk, eggs, strawberries, fish, tomatoes Consult allergist to identify allergen and avoid it.

Drug allergies to aspirin, penicillin, vaccines, and anesthetics Avoid the drugs. A doctor can provide alternatives.


25

Athlete’s foot is probably the most common foot complaint. It is a fungal infection, like ringworm, that can affect almosteveryone, although small children seem immune to it.

The fungus settles in the moist, sweaty areas between thetoes, where it lives on dead skin, which the body sheds every day.Athlete’s foot may cause inflammation and damage to the livingskin. The first signs are irritation and itching between the toes,and then the skin begins to peel. The condition may smellunpleasant. In more severe cases of athlete’s foot, painful redcracks appear between the toes and even the toenails canbecome infected. The nails become either softer or more brittleas the fungus invades the nail substance. In extreme cases, the whole foot swells and blisters.

The fungus that causes athlete’s foot can be present on floorsand in clothing. People with sweaty feet are particularly likely to develop it. Wearing plastic shoes, which prevent air fromcirculating around the feet, makes the problem worse. Lockerrooms and showers are breeding grounds for the fungus.

Treatment for athlete’s foot is simple and soon successful.Antifungal creams should be applied daily while the conditionlasts, and for two or three weeks after the symptoms havedisappeared, to prevent it from coming back. If the conditiondoes not clear up, the person should see his or her doctor, whomay prescribe a drug to take by mouth. To prevent athlete’s footfrom recurring, the feet, shoes, and socks should be dustedregularly with antifungal powder and the feet should always be washed and dried carefully. Clean cotton or wool socks (not nylon socks) should be worn every day.

Athlete’s Foot

In severe cases of athlete’s foot, the skinbetween the toes becomes painful, red,and cracked. The fungus responsible for the infection grows readily in these warm.moist areas, feeding on dead skin cells.

blisters • feet • podiatry • skin • sweat

SEE ALSO

I have a severe form of athlete’sfoot that keeps recurring. Willmy feet be permanently scarred?

No, because the fungus causingathlete’s foot lives only on thesuperficial layers of the skin,eating dead skin cells.

Can athlete’s foot spread to other parts of the body?

The athlete’s foot fungus can live on various parts of the body but is not contagious and is unlikely to spread. However,there is a condition similar toathlete’s foot that can affect thehands. That should be diagnosedand treated by a doctor.

My sister has athlete’s foot. Canshe infect the rest of the family?

Not if all family members washand dry their feet carefully using separate towels and use antifungal powder.

Q & A


26

The autonomic nervous system controls all the body functionsthat people never really think about, such as heartbeat, fooddigestion, and breathing in oxygen from the air.

Every day, the body does many things that are taken forgranted. Every heartbeat and every breath keeps the body alive,but these events happen automatically, without any thought.The control mechanism for these automatic body processes is the autonomic nervous system.

Inside the nervous systemThe nervous system is the body’s communication center. Nervecells are like living electrical switches, which respond to signalsfrom the body’s central processing unit—the brain. The brain is a mass of billions of tiny nerve cells. These cells process all the signals from the outside world and decide what to do about them.

The things that people think about, such as opening a door or pressing a button, are processed in “higher” parts of the brain. Things people do not think about, such as blinking and pumping blood around the body, take place in the “lower” parts of the brain and spinal cord, which together are called the autonomic nervous system.

How nerves workThe nervous system works by sending electrical signals downnerve fibers, or axons, from one nerve cell to the next. The axonsare the “wiring” through which signals pass along the body, to and from the brain. The nerve cells at the end of the axonstransmit or receive the electrical signals. There is a small gapcalled a synapse between the ending of an axon and the nervecell itself. Chemicals called neurotransmitters carry the electricalsignal across the synapse. The neurotransmitter then stimulatesthe neighboring nerve cell to produce the electrical signals thatpass through the next axon, and so on.

Sympathetic and parasympathetic nervesIn the autonomic nervous system, there are two types of nerves:sympathetic and parasympathetic nerves. Each one uses adifferent type of neurotransmitter and has a separate effect onthe body. For example, parasympathetic nerves in the lungs canmake the airways leading to and from the lungs grow narrower.Sympathetic nerves in the same area can make the same airwaysgrow wider. In all cases, parasympathetic nerves are controlled bya neurotransmitter called acetylcholine. Sympathetic nerves arecontrolled by a neurotransmitter called norepinephrine.

AutonomicNervous System

Why is it that I often feel sleepyafter I have eaten?

Many digestive processesdepend on the autonomicnervous system. It has twosubsystems: the sympathetic,which is the system of actionand activity; and theparasympathetic, which is concerned mostly withrelaxation. Digestion iscontrolled mainly by theparasympathetic system, so when it is at work, thesympathetic system is less activethan usual. This minor degree of parasympathetic overactivityand sympathetic underactivitycombines to produce sleepiness.

Why does my hair literally “standon end” when I am frightened?

Fear influences the sympatheticautonomic nervous system,which controls the small musclesthat lift the hair off the skin. The pupils will also widen, andsweating may start, particularlyin the palms of the hands, wherethe sweat glands are controlledmore directly by the sympatheticnervous system than those inother parts of the body.

Q & A


27

Autonomic Nervous System

Everyday problemsOne minor problemassociated with theautonomic nervous systemis extremely common—fainting. That occurs whenparasympathetic nerves goon overdrive and make manysmall blood vessels growwider. The blood pressurethen falls and blood flowsaway from the brain to thebody, making the person fallunconscious. To recover froma fainting attack, it is best to lie flat so that the bloodflow returns to normal.

Asthma is a much moreserious problem. Whensomeone has an asthmaattack, parasympatheticnerves leading to theairways in the lungs grownarrower. That makes it verydifficult for the person tobreathe. Inhaling a drugsimilar to norepinephrineboosts the sympatheticnervous system, thuswidening the airways.

Serious nervous disordersMany diseases can affect the autonomic nervous system,including AIDS, diabetes, and tumors. Nerve damage can alsooccur through alcohol and drug abuse. Symptoms of autonomicnerve damage include fainting, fatigue, dizziness, and reducedsweating. Drugs are usually used to control or block nervepathways leading to the diseased organ. That function copies the effects of natural neurotransmitters. In some cases, surgery is necessary: nerves are cut to relieve symptoms of the condition.

SEE ALSOasthma • blood pressure • diabetes • fainting • heart •nervous system • spinal cord • tiredness

The parasympathetic nervous system,which is controlled from the brain andlower spinal cord, interacts with thesympathetic nervous system, which is controlled from the spinal cord, to maintain a balance of the body’sunconscious activities.

cerebellum

brain

iris

bronchi

liver

stomachadrenalgland

smallintestinecolon

bladderspinal cord

sympathetic systemparasympathetic system

salivary gland

heart andblood vessels


28

The back is such a complicated structure that it is easily strainedor damaged. Backache is one of the most common of allcomplaints. The flexible spine is normally held in position by the muscles of the back and abdomen. Standing or sitting badly,twisting around, lifting heavy objects, and digging all put strainon the muscles, ligaments, and joints of the back.

Structure of the backThe back runs from the base of the neck to the base of the spine. The spine is a column of small bones called vertebrae.There are 12 thoracic vertebrae at the back of the chest; fivemuch larger vertebrae in the lumbar region (in and below thecurvature of the waist); and five fused vertebrae, called thesacrum, that form a triangular bone at the base of the pelvis. At the base of the spine is the coccyx, which consists of three to five small vertebrae. At each end of the spinal column is aring, or girdle, of bones that provides support for the limbs. At the top of the spinal column, the arms are attached to thepectoral girdle, which consists of the collarbone, the shoulder

Backache

People who have a tendency to backachecan help themselves by standing andsitting correctly, with a straight back. A relaxed posture, rather than a stiff,strained position, is ideal.

Will riding my bicycle to schoolbe bad for my back?

No, because on a bicycle yourbody weight is supported andbalanced by the shoulder girdleand the pelvic girdle, with thespine between them. Thecontinual movement of cyclingalso keeps the back supple andwell exercised. However, adjustthe handlebars and saddle to suit your height and theproportion of your limbs forcomfort and to reduce possiblestrain on the back.

My sister wears shoes with heels.Will they be bad for her back?

Yes. High-heeled shoes changethe body’s balance and weight-bearing axis, tilting the lowerspine and pushing the weightforward. That puts excessivepressure on the lower part of the lumbar region, causing painand faster aging of the joints,including the knee joints.

Q & A


29

Backache

blades, and the muscular attachments to the spine. The pelvicgirdle at the base of the spinal column is made up of the pubicbones, the iliac bones, and the sacrum.

Types of backachesMost backaches have no obvious cause. They are the result ofsome strain that has caused the muscles to go into a spasm.Stress, too, can cause the back muscles to tense and ache. Many people have backaches caused by fibromyalgia, particularlyin their shoulders. Fibromyalgia is pain and stiffness in themuscles, particularly those in the neck, shoulders, chest, back,buttocks, and knees. Low back pain (lumbago) is often caused by lifting, twisting, or digging and can come on suddenly ordevelop over hours or days. It can be so severe that the patientcannot move the back at all. It is probably caused by strainedmuscles and ligaments and muscle spasm, but it can also be due to intervertebral disk prolapse (slipped disk).

Slipped disks are a very common cause of backache. There is a disk between each pair of vertebrae that prevents frictionand eases movement. These disks are prone to wear and tear as time passes, however, and they become thinner.

Osteoporosis, in which the bones become increasingly weakand brittle, can cause the vertebrae to fracture. As a result, older women become shorter as their vertebrae crumble and experience pain as the spinal nerves are compressed.

Ordinary back pain eases in a few days; low back pain may last longer. A doctor may prescribe painkillers and musclerelaxants. A slipped disk may last for a number of weeks, and

the doctor may tell the patient to spend a week or two lying flat in bed. Severe cases may be helped by physical therapy ormanipulation by an accreditedosteopath or licensed chiropractor,who can tell if anything in theback is out of place.

Sleeping on a firm mattress, or with a board under themattress, gives the back a chanceto rest in the correct position.

SEE ALSOchiropractic • muscle • pain • posture • skeletal system

• slipped disk • spinal column

Top: The scapula and clavicle form the pectoral girdle; the ilium and ischium form the pelvic girdle.Bottom: Close-up of vertebral disks in the lumbar region of the back.

normal diskbetween lumbarvertebrae

clavicle

scapula

humerus

ilium

lumbarvertebrae

thoracicvertebrae

sacrum

ischium

femur

coccyx

slipped diskpressing onspinal cord


30

Balance is the even distribution of weight, allowing one to stand upright and steady. Humans walk on two legs, relying on a highly developed sense of balance to keep them fromfalling. The body’s balancing mechanism is located inside theears. The ears not only hear sounds but are also responsible for moment-by-moment monitoring of position and movementsof the head. If the exact position of the head is monitoredcorrectly, the body can adjust itself to stay balanced.

Balance is a basic skill needed in practically every aspect of life.It is so essential that humans spend their first two to three yearsof life trying to master balance. It takes another year for childrento stand on one leg and even longer to do more balancingexercises, such as walking on a narrow beam. Balance is alsocritical for any sport, from soccer, tennis, and rock climbing to gymnastics and dance. Being able to sense one’s position and balance is the key to being good at sports.

The inner earThe inner ear tubes that are responsible for balance are wellprotected by the bones of the skull. Inside the inner ear is anetwork of tubes filled with fluid at various levels and with

Balance

When the body moves, fluidin the semicircular canalscauses the hairs in thejellylike mass to bend. Thenerves to which the hairsare attached alert the brainto rebalance the body.

My baby sister can balance wellbut prefers to crawl rather thanwalk. Is this normal?

Your sister may need morepractice at balancing beforewalking. At the moment, she issure she can crawl, so this is themost obvious way for her to getaround. She’ll walk when she isconfident that her body is ready.

Q & A

semicircular canals

semicircularcanals

saccule

outer ear

ear canal

tympanicmembrane(eardrum)

eustachian tube

middle ear

utricle

hairs

fluid

nerve

jellylike mass


31

differing angles. The tubes most directly involved in balance are the utricle, the saccule, and the semicircular canals.

The utricle and saccule are involved in detecting the positionof the head. Each of these tubes contains a pad of cells with finehairs called hair cells that are coated with a jellylike fluid. Whenthe body is upright and the head is still, the hairs remain still orunbent, and a resting signal is sent to the brain. If the head turns,the fluid moves inside the tubes, bending the hairs with it in thesame direction as the head. Bending the hairs prompts nerveimpulses that tell the brain the head is moving. When the headleans forward, backward, or sideways, the hairs bend in differentways. New messages are sent to the brain, telling the muscles of the body to adjust position. If a child starts to run, the hairsare pushed back as though the child were falling backward. Thebrain receives this information and sends signals to the musclesto make the body lean forward and restore balance.

Above the utricle of the ear are three semicircular canals. At the base of each canal is an oval mass of jelly containing thetips of sensitive hairs. The canals pick up information aboutwhen the head starts and stops moving. That is important inquick movements. Unlike the utricle and saccule, the fluid insidethe semicircular canals stays still, pushing against the hairs. The hairs send messages to the brain to take action. Sometimes,even when the head stops moving—for example, after someonehas been spinning around—the fluid inside the semicircularcanals continues to move. That causes dizziness. For instance,when dancers are first learning to pirouette in ballet, they oftenget dizzy from the continual turning. However, as they practice,their ears and body get used to this motion.

The cerebellumThe part of the brain that is most responsible for directing the action of the muscles in keeping the body balanced is thecerebellum. The cerebellum collects information not only fromthe balancing organs in the ears, but also from the eyes, neck,spine, arms, and legs. These systems work together to keep aperson balanced. For example, when playing tennis, an athletemust keep his or her eyes on the ball and run to keep up with the ball, while keeping the rest of the body ready to respond to the ball’s position. All of the body’s balancing systems must be used to carry out these actions.

Balance

body systems • fainting • muscle • sports • tiredness

SEE ALSO

When a child is balancing on a climbingframe, the inner ears are responsible for monitoring the position of the head and body. The ears send messages to the brain to adjust the body’s positionand keep it upright.


32

Metabolism encompasses all the chemical processes in the bodythat allow a person to grow, survive, and reproduce, using foodas fuel. The rate of metabolism varies according to the amountof energy a person expends and from one person to another. Theminimum constant rate of metabolism that is measured severalhours after eating, when the body is at rest and in a room atnormal temperature, is the basal metabolism. That is the energyneeded to keep the body running. Metabolism consists of twodistinct processes—catabolism and anabolism. Catabolism is the breakdown of complex substances in food into simpler ones,releasing energy in the process. This energy is converted intouseful work through muscle activity. A certain amount of energyis lost as heat. In anabolism, food materials are adapted to bestored as energy or used by the body in growth, reproduction,and defense against infection. The term anabolic refers to thebuilding up of complex substances from simple substances.

An adult whose food intake is too low uses anabolic foodreserves and loses weight. If more food is eaten than is needed,the surplus energy is stored as fat. A person doing a lot of heavywork or strenuous exercise needs more energy, and thereforemore food, than a secretary. A child needs more food than thatrequired simply to provide energy, because the surplus is used ingrowing. People who have a low basal metabolic rate burn theirfood slowly and have to do extra exercise to avoid putting onweight. People with a high basal metabolic rate are usually ableto eat what they like without gaining too much weight.

BasalMetabolism

SEE ALSOanorexia and bulimia • calories • diet • exercise •food and nutrition • obesity • weight control

People expend different amounts ofenergy depending on their activities. Anaverage person burns 1,750 to 2,000 kJ(420–480 kcal) per hour playing tennis(left) and only 300 to 350 kJ (70–80 kcal)sitting at work (right).

EXPENDING ENERGYThe energy a person expends is measured in kilojoules (kJ); one kilojoule is equivalent toaround 4.2 kilocalories (kcal) or big “C’’ Calories. An average-sizeman has a basal metabolic rate ofaround 7,110 kJ a day (1,700 kcal);an average-size woman’s rate isaround 5,850 kJ a day (1,400 kcal).The rate varies between people.

I am no longer losing weight on my diet. Is this connected to my basal metabolism?

Yes. Less food causes the body to lower its basal metabolism in an attempt to slow down andconserve energy. That can causea plateau effect—no furtherweight loss can be achieved. Aregular routine of cardiovascularexercise helps raise the basalmetabolism and thus the rate at which calories are used.

Q & A


33

A black eye is a dark bruise and swelling around the eye. A blackeye normally looks a lot worse than it is. Despite the name, it isnot the eye that turns black but the eyelid and skin around theeye. A black eye is caused by a blow to the eye or nose. The eyeitself is normally not harmed, because it is protected by a ring of bone and flesh called the eye socket, or orbit.

Under the surfaceThe scientific name for a black eye is a periorbital hematoma.Periorbital means “around the orbit.” Hematoma is the medicalname for bruising and swelling. A bruise is created when the skin is damaged without being cut open. The damage breaks the blood vessels in the skin, and the red blood released beneaththe skin gives the skin its dark color. More blood rushes to thearea so the body can start to mend the damage. As a result, the bruise fills with liquid and swells.

Thin skinThe eye area bruises more easily than most parts of the body,because the skin is stretched around the eye socket and has onlya thin layer of soft tissue beneath. When this area bruises, thereis not much room for the blood, so it spreads out below the thin,stretched skin. That is why a blow to the eyebrow or nose canmake the whole socket and eyelid look bruised and swollen.

The eyelid might get so swollen that the eyebecomes closed. Whenthis happens, it isimportant to visit thedoctor so he or she cancheck that the eye itselfis not damaged.

Holding somethingcold on the sore eyefeels good and makesthe blood vessels in the area shrink, whichstops blood fromgetting to the bruisedarea and reduces theamount of swelling.

Black Eye

A black eye can be very painful but oftenlooks worse than it is. It usually takesaround a week for the bruising to heal.

bruises • circulatory system • ice therapy • pain • skin

SEE ALSO

Why is raw steak the traditionalremedy for a black eye?

A clean, raw steak providesmoisture, coolness, and softnessin a form that will mold itselfneatly to the shape of the eye. It has no other beneficialproperties and it is an expensivecompress. A cloth wrung out incold or iced water is just as goodand readily available at no cost.

The school dance is in five days.How can I disguise a black eye I just got playing basketball? I’ve already bought my dress!

You could wear sunglasses, but carefully applied makeupshould go a long way towarddisguising the black eye. Applyfoundation in a slightly lightercolor than your normal skin tone. Wear eye shadow in a color similar to the bruising.Remember that most black eyesgo away in six to eight days, so in five days’ time, the coloryou will have to cover will bemuch reduced.

Q & A


34

Blisters are swellings caused when fluid collects between theouter and inner layers of the skin. They are caused most often by friction, such as rubbing or chapping. Wearing shoes that donot fit properly and doing heavy work with the hands when theyare not used to it are two common causes of blisters. All types of burns, including a bad sunburn, can also raise blisters. Theheat and damage to the deep layer of the skin cause an almostimmediate outflow of fluid from the blood capillaries; the fluidthen lies in the form of blisters under the skin. Sunburn blisterstend to be small and numerous. The skin will start to peel a fewdays later. Other blisters are caused by bites and stings, illnessesincluding chicken pox, and infections. Cold sores are made up of a cluster of tiny blisters, caused by a virus called Herpes simplex.They sometimes appear on the lips or side of the mouth after a cold. If the cold is severe or the skin is exposed to too muchsunlight, the virus will multiply, and crops of blisters will form.

Symptoms and treatmentA common friction blister causes feelings of heat and pain, andby the time these symptoms have been noticed, a blister willhave formed. Similarly, a blister arising from a direct burnappears a few minutes after the accident. Blisters from stingsand bites appear more slowly and cause itching and a swelling of the surrounding skin. Chicken pox begins as small, dark redpimples, which within a few hours turn into blisters that look like droplets of water. Where there are multiple blisters with no symptoms, the cause is more likely to be eczema.

The common friction blister is rarely dangerous, but in othertypes of blisters there is a danger of infection. Bacteria can enterthe body and breed, forming pustules, which delay healing orspread infection. If large areas of the skin are blistered, there is also a risk that the body will lose a lot of fluid, causing thepatient to become seriously ill.

People with large blisters or blisters that appear for no knownreason should see a doctor. Other blisters should be kept cleanand covered. If the area will get more friction, the blister shouldbe opened with a sterile needle to let out some of the fluid.Otherwise, a blister should be opened only if it is really painful. To treat a friction blister, first cool and clean the area. A smalladhesive bandage can be used to cover a small blister.

Blisters

A large and painful blister like this oneshould be seen by a doctor. There is a highrisk of infection if such a blister is popped,because of the large size.

I have a blister on my heel.Should I pop it?

It is best to leave blisters as longas possible before popping them,because of the risk of infectingthe underlying skin. Some blisterswill be more comfortable if thefluid is drained with a sterile pinor needle by a doctor, but unlessthey cause discomfort, blistersare best left alone, covered by a small bandage. Large blistersneed medical attention.

Q & A

exercise • feet • pain • skin • sunburn

SEE ALSO


35

As the heart pumps blood around the body, the pressure of the blood in the arteries varies. Blood pressure is highest whenthe heart is pumping blood into the arteries (systolic pressure)and lowest when the heart is resting between beats (diastolicpressure). These two pressures are measured together inchecking a person’s blood pressure.

The “normal” level of blood pressure varies greatly from oneperson to another and increases as someone gets older. Foryoung and middle-aged adults, a pressure of 120 (systolic) and 80 (diastolic) is considered normal. That is written as 120/80. A blood pressure of 140/90 would be a little worrying; a pressure of 160/90 is definitely high and needs treatment.

Low and high blood pressureSome people have low blood pressure. That is nothing to worryabout, although it can make them feel dizzy, particularly if theystand up suddenly. Blood pressure can fall seriously low withcertain infections; when a person loses a lot of blood or is in shock after an accident; or after a heart attack.

High blood pressure, or hypertension, is common in peopleliving in the developed countries of the world and is a seriousproblem. The increased blood pressure damages the walls of the arteries and can lead to a coronary thrombosis, a heartattack, or a stroke. Arterial damage from high blood pressure can also lead to serious disturbances in the functioning of the brain, eyes, kidneys and other organs, and muscles.

As a precautionary measure, everyone should have his or her blood pressure checked regularly by a doctor.

The pulseThe pulse is the regular throbbing that is made by the heart as it pumps blood through the arteries and around the body. Thepulse can be felt in a number of the arteries that lie near thebody’s surface, including the artery on the inner surface of thewrist. Taking someone’s pulse tells a doctor whether the heart is beating regularly and how fast and how strongly it is beating.The pulse also gives information about the condition of theperson’s arteries. The normal pulse rate is around 70 to 80 beatsa minute in an adult. That rate can rise to more than 120 beats a minute with exercise or as the result of a fever.

Blood Pressure

The minimum (diastolic) pressure is taken when the heart has filled withblood from the head, arms, lungs, and body and is fully distended.

The maximum (systolic) pressure is measured when the heart is pushingthe blood out into the body and lungs.

circulatory system • heart • heart attack • stroke

SEE ALSO


36

The organs of the body are major units such as the heart, lungs,stomach, liver, kidneys, skeleton, and brain. Each organ is made of tissues, which in turn are made of cells. The cells are complexcollections of cell organs (organelles) bathed in a chemical-richfluid. Each cell contains deoxyribonucleic acid (DNA), whichincorporates the genes that determine the characteristics, suchas skin and eye color, that children inherit from their parents.

There are several main types of tissues, and each organcontains at least one kind oftissue. Epithelial tissues, forexample, are sheets of tissuesthat cover or line the organs of the body. Epithelial tissuesinclude the skin, which coversthe outside of the body.

Connective tissues are thosethat connect or fill out thestructures of the body. Theyinclude ligaments and tendons.

Skeletal tissues include allthe bones of the skeleton andthe soft gristle known ascartilage. Muscle tissues enablethe body and its componentparts to move and work.

Nervous tissue is thecommunication network of the body, linking all the partsand carrying messages to andfrom the brain.

Body Systems

Right: The human body consists of anumber of systems, each with its own jobto do, yet all working together as a unit.

Far right: Muscle tissue consists of fibersthat contract. Epithelial tissue lines andcovers the surface of internal organs.

Can people’s state of mind reallyaffect their immune system andmake them prone to illness?

Yes. Current medical thinkingholds that the interaction of themind and all body systems is sointimate and interdependentthat hardly anything can happenin one area without affectinganother. This certainly holds truefor the emotions and the immunesystem. There is a disciplinecalled psychoneuroimmunologythat studies this relationship.

What is it about the “funnybone” that causes such a strangeand painful sensation if I hit it?

This sensation concerns theulnar nerve, which passes behindthe elbow and into the forearm.A slight knock here can cause a volley of signals in the nerve’ssensory fibers, which can beexcruciatingly painful.

Q & A

epithelialtissue

muscletissue


37

The skeletal systemThe skeleton, or skeletal system, is the framework that supportsthe body. The bones that form the skeleton are linked by flexiblejoints so that the body can bend and move. The bones are held in place at the joints by bands of tissue called ligaments.

The skeleton is made mostly of bone. While a baby is in theuterus (womb), however, its skeleton is made of a softer, moreflexible substance called cartilage. As a child grows, the cartilageis gradually replaced by hard bone. Adults still have cartilage inthe lower part of the nose and ears, at the ends of long bones,and between the front ends of the ribs and the breastbone.

The muscles that enable a person to move make up most ofthe body’s flesh. Many muscles, known as skeletal or voluntarymuscles, are attached to the bones by cordlike tissues calledtendons. These muscles are stimulated by messages from thebrain that are carried along the nerves. As a result, musclemovement can be controlled. Other muscles, known as smooth or involuntary muscles, work automatically. They include themuscles of the digestive system and the heart. Heart muscleshave the power to contract spontaneously and rhythmically.

The circulatory system The heart is a pump that drives the blood around the body.Together, the heart and blood make the circulatory system. Bloodis used to carry food and oxygen to all the cells of the body andto take away their waste products. The blood flows through a complicated network of tubes, known as the blood vessels,which forms the body’s plumbing system. This pipeline system of vessels is extremely long; in a full-grown man, it can totalmore than 60,000 miles (97,000 km). The system carries about10 pints (4.7 l) of blood. The blood picks up oxygen from the lungsand is then pumped through the biggest blood vessels, known as the arteries, to all parts of the body. The arteries divide intosmaller blood vessels, called arterioles. From there, the bloodflows through fine tubes called capillaries to all the body’stissues. The capillaries distribute oxygen and other nutrients to the tissues and collect waste products. The blood then flowsback to the heart through a series of medium-size tubes, knownas the veins. Blood is returned to the lungs, where it gets rid of carbon dioxide and picks up fresh oxygen.

The immune system All around are bacteria and viruses that can make people ill. The body’s immune system helps protect people against disease.The first barrier in the immune system is provided by the skin.

Body Systems

Skin is a kind of epithelial tissue thatcovers the surface of the body. The surfacethat can be seen is made of dead cells (1).Below is living tissue containing nervecells (2), sweat glands (3), hair follicles (4),fat cells (5), and blood vessles (6).

1

2

3

4

5

6


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However, germs can enter through wounds or be injected byinsects such as mosquitoes. Germs can also enter the lungsthrough breathing if they are not trapped and expelled in themucous lining of the respiratory system. Once inside the body,germs encounter white cells in the blood, which attack and killthem with the aid of antibodies. If germs are swallowed, acids in the digestive system help destroy them. If the immune systembreaks down, the consequences are serious.

The respiratory systemThe organs of the respiratory system consist of the mouth andnose, trachea (windpipe), and lungs. Just as the heart is a pumpfor the blood, the muscles between the ribs and the diaphragmact as pumps for air, contracting to increase the volume of thechest so that air is drawn into the lungs. Like the heart, thismechanism works automatically, pulling in fresh air, rich inoxygen, and expelling waste air that contains carbon dioxide.Unlike the heart, the lungs are not completely automatic.

Oxygen absorbed from the air is used by the body to convertfood into energy. The converted food is carried to the cells by the

Body Systems

Below left: The skeleton is made of hard,living bone tissue. The bones are hingedat joints. The knee joint allows up-and-down, but not sideways, movement. Theball-and-socket hip joint allows the thighbone to rotate. The joints between thebones of the toes are highly flexible.

Below middle: The power to move thebones is provided by muscles. A singlemuscle acts not alone, but with one ormore other muscles. When a musclecontracts, it pulls on a bone; its opposingmuscle relaxes to let the bone move.

Below right: Blood supply is vital to bones,muscles, and all the other tissues. Bloodflows through blood vessels, carrying food and oxygen to the cells and wastematerials away from them.

SKELETON

kneejoint

toe joints

anklejoint

hip joint

MUSCLES BLOOD SUPPLY


39

blood. In the cells, waste carbon dioxide gas is picked up by theblood and returned to the heart. It is then pumped to the lungsand expelled from the body. This process is called respiration.

Breathing is known as external respiration. Air is drawn inthrough the nose and filtered to get rid of harmful substancessuch as dust and bacteria. As air goes down through the tracheato the lungs, it is warmed and moistened.

The trachea divides into two smaller pipes called bronchi,located inside the lungs. In turn, the bronchi split into a networkof smaller tubes called bronchioles. The bronchioles branch intotiny sacs, called alveoli, where oxygen is delivered to the bloodand carbon dioxide is returned.

The digestive systemFood and drink are the body’s fuels and the raw materials fromwhich the body can replace or repair worn-out and damagedcells. Before the blood can take these supplies to the cells, theymust be broken down into a form in which they can be used. This process is called digestion. Digestion begins in the mouthwhen the food is chewed to break it into small pieces beforeswallowing. The saliva in the mouth is the first of many powerfulsubstances that act on the food. From the mouth, the foodpasses down a long tube, called the esophagus, to the stomach.Muscles in the stomach wall knead the food to soften it further,and chemicals called gastric juices act by breaking down proteins.

Body Systems

A variety of white blood cells performingtheir various jobs: swallowing bacteria (1);reacting to antibodies and histamine (2);releasing heparin to stop blood fromclotting (3); and releasing antitoxin to neutralize antibodies (4).

The respiratory system consists of thenose (1), mouth (2), trachea, or windpipe(3), and lungs (4). During breathing, mostof the work is done by the diaphragm (5),a large sheet of muscle that lies below the lungs. The lungs are protected by therib cage (6).

bacteria

1

2

3

antibodies

heparin

histamine

antibody

antitoxin 4

12

3

4

56


40

From the stomach, the partly digested, semiliquid food passesinto the intestines. First, it enters the small intestine, a coiledtube around 20 feet (6 m) long, where the food is finally brokendown into the form of fats, amino acids, and glucose. In thisstate, the food is absorbed into the bloodstream through tinyprojections, called villi, on the walls of the small intestine.

From the small intestine, what remains of the food passes intothe large intestine. Most of the useful substances have by nowbeen absorbed into the blood. The remainder is waste, includingroughage, such as vegetable fibers and seeds, living and deadbacteria, dead cells from the walls of the upper part of thedigestive system, waste gastric juices, and water. As this wastematerial passes through the large intestine, most of the water is removed, and the solid waste is eventually expelled from the body through the rectum and anus in the form of feces.

The urinary system Waste substances that have been broken down in the body arecarried by the blood to the kidneys. They remove waste materialsand surplus water from the blood, producing a liquid known asurine. Urine then passes, via the ureters, into the bladder, where it is stored. Once there is a sufficient buildup of urine in thebladder, the body is stimulated to excrete it via the urethra.

The glandular systemThe glands are the body’s factories, making substances that thebody needs and processing waste products. There are two kindsof glands: exocrine and endocrine. Exocrine glands secrete theirproducts into ducts, or channels, that carry them inside or outsidethe body. Exocrine glands include the liver, tear ducts, salivary anddigestive glands, and mammary glands (which produce milk).Endocrine glands are ductless; they secrete hormones straightinto the blood. They include the pituitary gland, thyroid gland, andadrenal glands. These hormones control growth, reproduction, therate at which food is burned, the level of blood sugar, and thebody’s emergency response to fear and stress. Hormones can alsobe released by other organs, such as the brain, the kidneys, and the placenta, or fetal life-support system, in a pregnant woman.

The nervous system and sensesThe nervous system is the control mechanism for the body. Itscentral switchboard is the central nervous system (CNS), whichcomprises the brain and the spinal cord. The central nervoussystem receives and interprets messages from the rest of thebody and sends instructions through nerves to the muscles,

Body Systems

This diagram shows the digestion of a cheese sandwich. Proteins, fats, andcarbohydrates are broken down intosmall molecules and absorbed into theblood to be used by the cells. Digestivejuices in the mouth (1) act on the food,which passes into the stomach (2) and on to the duodenum, the first part of the small intestine (3), and the jejunum(4) and ileim (5). The broken-down foodpasses through the intestine walls. Wastematter enters the large intestine (6),where water passes into the blood. Finally, waste passes through the rectum(7), which is the end of the intestine, and out of the body.

7

65

43

2

1


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organs, and glands. The nerves are like telegraph wires, alongwhich the electrical messages travel to and from the body’ssenses. The senses link the brain with the world outside the body.

Humans are sensitive to sights, sounds, tastes, smells, touch,heat, cold, hunger, thirst, tiredness, and pain. The eyes are theorgans of sight. The ears hear sounds and help people maintaintheir balance. Taste and smell are linked to the digestive system.Aromas trigger the saliva needed for digestion. People’s sensestell them when the body needs to have food or rest, when itneeds to avoid danger, or when there is a malfunction or pain.

The reproductive systemsA man’s and woman’s reproductive organs enable a male spermto fertilize a female egg to produce a baby. Women have ovaries,which produce ova (egg cells). Once a month, one or more ovapass down the fallopian tubes to the uterus, where the egg canbe fertilized. Men have testes, glands that produce sperm cells.

Body Systems

Above: The body removes waste throughthe skin (water and salt), lungs (carbondioxide), liver and gallbladder (bile),kidneys (urea), and bowel (feces).

Right: Glands regulate metabolism, aiddigestion, produce sweat, and controlgrowth and reproduction.

Far right: The central nervous systemconsists of the brain and spinal cord, from which pairs of nerves radiate all over the body to form the peripheralnervous system.

Below: The female reproductive systemconsists of the ovaries, fallopian tubes,uterus (womb), and vagina.

skin

lung

liver

kidney

bowel

pituitarygland

salivaryglands

thyroidgland

lymphnodes

adrenalgland

pancreas

ovary

brain

spinalcord

ovaries

fallopiantube

uterus

vagina

autonomic nervous system • circulatory system •digestive system • glands • heart • ligaments • muscle •nervous system • respiratory system • skeletal system •skin • tendon

SEE ALSO


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A bruise is a patch of dark or discolored skin that can occur on any part of the body. It is caused by a bump or blow thatdamages the small blood vessels (capillaries) within the lining of the skin. Blood oozes out of the capillaries, giving the skin the familiar dark red color of a bruise. The area swells as serum(watery fluid) from the blood collects there. The platelets in the blood start the clotting process, which limits the area of the bruise and plugs the leaking blood vessels.

A bruise takes about three to six days to heal. During this time, the body reabsorbs the blood, and the bruise fades tobluish purple, greenish blue, and then yellow, before fading away completely. Small bruises are best left to heal on their own. Pressing gently on the bruise with a cloth soaked in coldwater or with an ice pack limits the pain and swelling.

ComplicationsA bruise under a toenail or fingernail should always be shown to a doctor, because the tiny bone beneath the bruised nail maybe broken. The doctor may decide to release the blood fromunder the nail to relieve pain and reduce the risk of infection.That helps stop the whole nail from turning black. Very large and swollen bruises should also be seen by a doctor.

When bruises occur with open wounds or lie over bonystructures such as the skull and ribs, they may hide a fracture. In the case of bruises to the face and scalp especially, it is alwaysadvisable to see a doctor to rule out any underlying fracture

or other damage to these areas.Some people bruise more easily

than others. Children, for example,often have many bruises, usuallybecause they are likely to have many minor falls and bumps. Elderly people also bruise easily,because their skin is less elastic and their capillaries becomeincreasingly fragile with age.

Anyone who seems to bruise very easily and with little apparentcause should be checked by a doctorto eliminate other problems.

Bruises

A bruised fingernail may cover a smallbroken bone, so medical advice should be sought if a nail is injured.

I bruised my shin really badlywhile playing football. Is itpossible that I have damagedthe bone in some way?

Although the shinbone (tibia) isvery near the surface of the skin,it is strong and does not fractureeasily. Nevertheless, you shouldsee a doctor if you are worried.

I have noticed that my bruisesoften take longer to fade thanother people’s bruises do. Whatis the reason for that?

Several factors could be addingto the delay. Your body’s clearingmechanism may be slow inreaching the affected area, or thebruising may be extensive and somay take longer to clear anyway.Alternatively, if a hematoma (a localized collection of blood)occurs, you may need medicalhelp. Finally, there is a slightpossibility that you may have a deficiency either of vitamin Cor of blood platelets, which willslow down the clotting process.You should see your doctor.

Q & A

SEE ALSOblack eye • circulatory sytem • fractures and

dislocations • ice therapy • skin

NF_MC Bind_Up_pp42_83.qxd:Nutrition And Fitness 4/29/10 5:38 PM Page 42

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Calcium is a mineral. Together with the mineral phosphate, it isthe basic constituent of bones and teeth, and it gives them theirstrength. Calcium has other important functions in the body. It is essential for muscle contraction and for the transmission of nerve impulses from nerve endings to muscle fibers. Calciumalso helps blood to clot and is required for cell functioning.

The body absorbs calcium from food. During digestion,calcium passes through the intestines into the blood. Excesscalcium is excreted in the urine. The remainder is stored in thebones and teeth or reabsorbed into the bloodstream. Parathyroidglands in the neck produce parathyroid hormone and controlcalcium levels. If calcium levels are low, parathyroid hormone acts on the bones and teeth to release more calcium and to reduce loss in the urine. If calcium levels are too high, less parathyroid hormone is produced.

Milk, cheese, eggs, fish, and meat are the richest sources of calcium and should be included as part of a balanced diet.

Calcium

Is it dangerous to eat too muchcalcium in my food?

No. The body regulates how muchcalcium it requires and absorbsthe correct amount from yourblood. Excess calcium is passedout in the urine. However, takingtoo many vitamin D pills canupset the balance. If theabsorption system goes wrong,kidney stones can result. A low-calcium diet helps avoid this.

My grandmother, who is in hersixties, recently broke her arm. Is it possible that her bones haveweakened as she’s grown older?

Yes. The estrogen present inwomen before menopause helpsbuild up calcium in the bones.After menopause, osteoporosis(thinning of the bones) maydevelop. Your grandmother musthave an adequate diet. Extracalcium and biphosphonatedrugs will also improve hercondition.

People need calcium throughout life to keep their bones and teeth healthy. The main dietary sources of calciuminclude milk, cheese, eggs, meat, fish, and leafy green vegetables.

Q & A

SEE ALSOdiet • dieting • food and nutrition • glands • minerals

• vitamins


44

The body needs energy for all its activities—sitting, running,breathing, and digesting. People get this energy from the foodthey eat. The energy value of food is measured in kilocalories. Onekilocalorie is equivalent to the amount of heat needed to raise thetemperature of one kilogram of water by one degree Celsius.

The number of kilocalories that people need depends on howmuch energy they use. An active person such as a coal miner,construction worker, or athlete needs more kilocalories thansomeone who sits at a desk all day, such as a student, doctor, or office worker. Drivers also need fewer calories.

Energy needs also vary according to age, sex, body size, climate,and health. It has been estimated that about 2,000 kilocaloriesper day are needed to keep the body functioning normally. Forexample, a woman needs between 2,100 and 2,400 kilocaloriesper day; a man needs between 2,700 and 3,200 kilocalories perday. However, these figures are an average guide only; they willvary with the age and weight of the individual concerned andwith the amount of exercise taken outside work.

Protein, carbohydrates, and fat all provide energy. Proteins and carbohydrates yield around 4 kilocalories per gram; fats yield around 9 kilocalories per gram. Kilocalorie intake alsodetermines weight. If a person consumes more kilocalories than needed, the excess is stored as fat.

Calories

CALORIES USED IN EVERYDAY ACTIVITIES

CALORIES USEDACTIVITY PER HOUR

Sleeping 65Sitting 75Standing 110Typing 140Walking slowly 200Running 400Swimming 500Walking upstairs 1,100

Which exercise is best forburning calories?

It depends on what exercise youprefer and how much time youhave. For example, burning off an apple (about 100 calories)would take 20 minutes ofwalking, 12 minutes of bikeriding, 9 minutes of swimming,or 5 minutes of running. Burningoff a hamburger (about 350calories) would take 67 minutesof walking, 43 minutes of bikeriding, 30 minutes of swimming,or 18 minutes of running. Bycounting calories, you will have a better idea of how to adjustyour exercise schedule.

Q & A

carbohydrates • diet • fats • protein • weight control

SEE ALSO

SOME CALORIFIC VALUES

BeefsteakBrown riceButterCabbage (boiled)CheeseFish (cod)OrangesPotatoes (boiled)Sugar (white)WalnutsWhite breadWhole milkWhole wheat flour

250100700

15400100

70100395350200

65340

56.911.713.995.737.0

65.064.8180.0

a trace5.0

38.287.015.0

20.46.20.41.3

25.420.50.62.5

a trace 15.07.83.4

13.5

20.31.0

85.1a trace

34.58.3

a tracea trace

0.064.4

1.33.72.5

0.086.5

a trace1.1

a trace3.66.415.9

99.915.6

52.74.8

69.0

Type of food

CALORIES

PER 100 g

% WATER

CONTENT

% PROTEIN

CONTENT

% FAT

CONTENT

% CARB.

CONTENT


45

Food consists of three main groups: proteins, fats, andcarbohydrates. Carbohydrates are the main source of energy for the body because they provide the fuel, glucose, on which all cells depend. These cells play a vital role in the properfunctioning of the internal organs and the nervous system and in heart and muscle contraction. Carbohydrates are made byplants in a process called photosynthesis. Humans get this typeof food from certain plants or from animals that feed on plants.

There are two main types of carbohydrates: starch and sugar.Most carbohydrates eaten are starches, the stored food in plantseeds. Starch is made of complex chains of molecules linked withunits of glucose. Starch is indigestible unless it is cooked. It ispresent in grains, vegetables, and fruits. Grains include whole-grain bread, rice, oatmeal, cereals, pasta, tortillas, and crackers.Sugars, including glucose, galactose, fructose, sucrose, andlactose, are present in all sweet foods, such as cakes, cookies,candies, and honey, and in sweet drinks. During digestion,enzymes in saliva and the intestines break down carbohydratesinto simple sugars such as glucose, which are absorbed into thebloodstream. Some glucose is transported to the liver, changedinto a form of starch called glycogen, and stored. As the bodyuses glucose, the stored glycogen is changed back into glucoseand released into the body to provide energy. This process iscontrolled by hormones, particularly insulin from the pancreas.

Carbohydrates

SEE ALSOappetite • calories • diabetes • diet • dieting • fats •food and nutrition • protein • sugars

French fries and an apple are both rich in carbohydrates. The apple is better,healthier and less fattening, not becauseof the starch in the potatoes but becauseof the fat used for frying them.

Why does eating a lot ofcarbohydrates make me gainweight but eating a lot ofproteins doesn’t?

The human body uses proteinsand carbohydrates in differentways. Carbohydrates are used forenergy; when they are not beingused, they are stored by the bodyas fat. Proteins are used to makestructural tissue (muscle, bone,skin), enzymes, some hormones,and neurotransmitters.Therefore, proteins are notstored by the body as fat.

Because she gains weight whenshe eats carbohydrates and fats,my friend claims that the twothings have the same caloricvalue. Is that true?

No. There are three basic foodgroups: carbohydrates, proteins,and fats. Carbohydrates andproteins contain roughly fourcalories per gram; fats containnine calories per gram.

Q & A


46

Celiac Disease Celiac disease is a particular condition in which food, especiallyfats, cannot be properly absorbed. Celiac disease is a geneticdisorder in which there is a sensitivity to gluten, the insolubleprotein present in wheat and other grains, which causes thestickiness in dough. Gluten is a mixture of two proteins: gliadin(which causes the problem) and glutenin. In people with thisgenetic mutation, the immune system is sensitive to gliadin,treating it as a foreign substance and developing antibodies to it, which attack the intestinal lining.

For digested food to be absorbed, a large surface area is needed.Although the small intestine is about 20 feet (6 m) long, itsinternal surface would not provide nearly enough area if it wereplain and smooth. To aid absorption, the surface area is increasedby millions of tiny, fingerlike protrusions called villi. Molecules of digested food pass through these villi to get into thebloodstream, before being carried to other parts of the body.

In celiac disease, the antibodies that attack the intestine havetheir most obvious effect on the villi, which become stunted and almost flat. The diagnosis can be positively confirmed byperforming a biopsy. The patient swallows a small, spring-loadeddevice (Crosby capsule), which is attached to a tube. When it istriggered, a sample of intestinal lining is retrieved through thetube. Microscopic examination reveals the defects in the villi.

Symptoms and treatmentCeliac disease causes weight loss, diarrhea, abdominal pain,anemia, bloating, distension, and bulky and fatty stools. Theremay also be bone softening from mineral and vitamin deficiency.These symptoms are due to food retention in the intestine andnutritional losses from failure of absorption. Treatment involves

excluding gluten fromthe diet. That is difficult,because gluten is usedwidely in foods such as bread, cakes, soups,sauces, hot dogs, andeven ice cream. Expertadvice is necessary. Extravitamins and mineralsmay be required.

The above biopsy shows normal villi, theprojections that line the small intestineand absorb nutrients. The stunted villi on the right show celiac disease.

My brother has celiac disease.Am I likely to develop it as well?

Celiac disease does run infamilies, though just how it ispassed on is not clear, and noteverybody with celiac diseasehas relatives who suffer from it.There is a controversial theorythat celiac disease can bebrought on by feeding infantsfoods containing gluten at tooearly an age, before theirimmune system can cope withforeign proteins. So it may bedue to a combination ofhereditary and dietary factors.

anemia • diet • digestive system diseases and disorders

SEE ALSO

Q & A


47

Chiropractic is a complex and highly specialized manipulativetherapy, which aims to correct disorders of the spine, joints, and muscles by the skillful use of the practitioner’s hands andwithout the use of drugs or surgery. It is similar in some ways to osteopathy. Chiropractic restores mobility to the spine andtakes pressure off the nervous system, which connects the spine with all the major organs of the body.

Spinal disorders are common and cause problems not only to the spine, but also to other areas such as the arms, hips, legs,and shoulders. They can cause back problems such as sciatica,lumbago, and slipped disk, and are even linked to complaintssuch as asthma, constipation, digestive troubles, and headaches.

Consultation and treatmentAn initial consultation lasts about 30 to 45 minutes, duringwhich the chiropractor takes a detailed case history anddiscusses the current problem before examining the patient.After taking the pulse, blood pressure, and blood or urinesamples, and checking reflexes, the chiropractor examines thespine while the patient sits, stands, walks, and lies down. He or she is able to spot any irregularities in the way the patientuses the spine and thus find out exactly where the spine ismalfunctioning. X-rays may be taken, to pinpoint the area of damage and the extent of the problem.

The first treatment usually begins at the second visit. Thechiropractor uses special manipulative techniques to restorenormal function to the musculoskeletal system, probably with a rapid thrust to the vertebra. The type of technique depends on age, build, and general health. Massage and trigger points areoften used to loosen knots and to warm tense, painful muscles.Ice treatments may be used to reduce pain and swelling.

Each manipulation, known as an adjustment, takes seconds,and the patient is asked to breathe deeply. Adjustment is notpainful, but there may be a cracking noise, which is often theworst part of the treatment. After treatment, the body may beslightly sore and may need a couple of days to settle down.

The number of sessions needed depends on whether theproblem is acute or chronic. Acute problems can be treatedrelatively quickly, usually with about 10 to 12 treatments over a period of six to eight weeks. Chronic cases take longer.

Chiropractic

A chiropractor uses manipulation, knownas adjustment, on a patient’s arm in anattempt to bring the joints and musclesof the body into alignment.

backache • muscle diseases and disorders • osteopathy

SEE ALSO


48

Cholesterol is a fatty substance that forms part of the wallaround the body’s cells and is used in the production of some of the body’s hormones. Normally, the body produces as muchcholesterol as it needs. Cholesterol is also eaten in certain foods.

Eating a great deal of cholesterol may cause high levels of the substance to build up in the bloodstream. That may causeproblems. Cholesterol is laid down in the walls of the arteries to cause the condition known as atherosclerosis, leading tohardening of the arteries, coronary artery disease, and strokes.

People at riskA number of factors contribute to the risk of arterial or heartdisease. Smoking and a family history of these conditions are as important as the level of cholesterol in the blood. People inthe United States get about 40 percent of their food energy from fats. Surveys of other groups of people who traditionally eat a less fatty diet suggest that if this figure was reduced tobelow 30 percent, cholesterol levels would probably be lowered.Such a reduction could be achieved by replacing fats withcarbohydrates (starchy foods such as bread, potatoes, and rice).Also, fats of animal origin—saturated fats—seem to increasecholesterol levels, whereas unsaturated fats, such as sunflower,safflower, and corn oil, do not.

Although not all scientists agree about the part played bycholesterol in the diet in causing atherosclerosis, it is sensible for people to avoid eating too much food that is high incholesterol. That includes foodstuffs such as butter, cream,

cheese, eggs, and meat.Fish and poultry containless cholesterol than beef, lamb, and pork.Unsaturated fats fromvegetables, such assunflower oil or olive oil, are healthier thansaturated fats fromanimals. Regular exercisealso lessens the risk thatcholesterol will build up in the artery walls.

Cholesterol

To maintain the right cholesterol level, it is important to eat a varied diet. Thefoods shown here are a healthy choice.

Does a high level of bloodcholesterol run in families?Several of my relatives have had heart attacks. Is there any connection?

Yes, there are some well-knownmedical conditions in whichabnormalities of the fats andcholesterol in the blood areinherited. People thus affectedmay need intensive treatmentwith both diet and drugs.

My brother has always beenteased about being fat. Does this mean that he has a highblood cholesterol level?

Not necessarily. People who arevery overweight consume morefood than they need, storing theexcess food energy in the formof fat. Their blood cholesterol,however, depends largely on themakeup of their diet, and yourbrother may also be eating the wrong kinds of foods. Try to get him to cut out fast food,ice cream, cakes, and candies.

Q & A

carbohydrates • diet • exercise • fats • heart • stroke

SEE ALSO


49

The term chronic fatigue syndrome is now most commonly usedfor a condition that involves severe fatigue and psychologicaldisturbance. The condition can be made worse by exercise.Chronic fatigue syndrome has had many names in the past,including myalgic encephalomyelitis, post-viral fatigue syndrome,epidemic neuromyasthenia, Otago mystery disease, and Icelandicdisease. Although detailed clinical investigations into thecondition have been carried out, in most cases they have failed to reveal any organic abnormality that could account for thesymptoms and the disablement.

Chronic fatigue syndrome is more common in women than in men. The fatigue experienced is not simply muscle fatigue andis quite different from the weakness experienced in disorderssuch as muscular dystrophy. In chronic fatigue syndrome, there is often a strong psychological element, with the suffererexperiencing mild to severe depression. As a result of theaccompanying depression, there has been a degree of skepticismsurrounding chronic fatigue syndrome. In part, this is becausedoctors suspect that the symptoms mask an underlyingpsychological problem. However, the cause or causes of chronicfatigue syndrome have yet to be identified. Although depressionis often present, it has not been established whether depressioncauses the disorder or arises as a result of the disorder. Othertheories link chronic fatigue syndrome with viral infections or suggest that it can arise as the result of a personal trauma,such as a death, separation, or loss of work.

Critical attitudes by doctors and others in the medical fieldhave not been helpful and have caused much distress tosufferers. Although it is important to establish whether or notthe condition has a physical cause, it is also vital to acknowledgethat people with the symptoms of chronic fatigue syndromedeserve help. Such a persistent disruption of normal livingindicates a disorder of the whole person.

Because of the failure to discover an organic cause, doctorshave not been sure how to treat the condition. In some cases,antidepressant drugs have been helpful. In others, cognitivebehavior therapy has been used. This type of therapy is notconcerned with the cause of the condition. Instead, cognitivetherapy concentrates on persuading the sufferer to live as normal a life as possible, often with excellent results.

Chronic FatigueSyndrome

Cognitive behavior therapy has been usedto treat chronic fatigue syndrome. Duringcognitive therapy, the patient is taught to analyze his or her thought processes,to identify negative trains of thought,and to adopt a more positive outlook.

My brother has been diagnosedwith chronic fatigue syndrome.My father thinks he is just lazy.Could my father be right?

Certain psychological statesmimic chronic fatigue syndrome(CFS) outwardly, but if a doctorhas diagnosed CFS in yourbrother, his condition will bemainly physical. However, CFSdoes cause some psychologicaldepression. Support from thosenear him, such as his family and close friends, will help.

Q & A

exercise • lethargy • muscle • tiredness

SEE ALSO


50

The circulatory system is the body’s transport system. It carriesfood, oxygen, water, and other essential materials around thebody to nourish and repair the cells; waste products are carriedaway and expelled from the body. The circulatory system consistsof the blood, the blood vessels (veins, arteries, and capillaries)through which blood moves, and the heart (a muscular pump,which continually pushes blood through the body).

Around 2 ounces (59 ml) of blood is pumped out of the hearteach time it contracts. Blood that is rich in oxygen and nutrientsstarts its journey from the left side of the heart, through a largeartery called the aorta. The blood flows from the aorta througharteries into smaller vessels called arterioles, which supply the

body’s tissues. From the arterioles,blood enters a network of minutevessels called capillaries. Oxygen and nutrients are transferred tocells, and carbon dioxide andwaste products are absorbed.

Deoxygenated blood then flowsfrom the capillaries into small veins(venules) to return to the heart. Theveins eventually merge into twolarge blood vessels, the venae cavae.From here, deoxygenated blood isdelivered to the right side of theheart, pumped into the pulmonaryartery, and taken to the lungs. Freshoxygen is absorbed into the bloodand the waste carbon dioxide isexpelled from the body by breathingout. The now oxygen-rich bloodflows through the pulmonary veininto the left side of the heart, andthe journey through the body beginsall over again. This complete circuittakes about 60 seconds. The heartbeats on average 70 times everyminute. It pumps an estimated8,000 gallons (30,280 l) of bloodaround the body every 24 hours.

CirculatorySystem

The circulatory system’s main arteries(red) and veins (blue) would cover manythousands of miles if they were removedfrom the body and laid out.

carotid artery

superior vena cava

jugular vein

aorta

renalartery

abdominalaorta

femoralaorta

renalvein

kidney

heart

hepatic veins(cross section)

inferior vena cava

SEE ALSOblood pressure • body systems • heart • oxygen •respiratory system


51

Most people drink coffee or tea. A cup of either drink may wakethem up in the morning or perk them up when they feel tired.Too much coffee and tea, however, is not always a good thing.Both beverages contain the mild stimulant caffeine. Caffeine acts on the central nervous system. It stimulates the brain and muscles and acts on the heart, blood vessels, and kidneys. In large amounts, it can cause insomnia (sleeplessness),restlessness, nervousness, a rapid pulse, and ringing in the ears.Caffeine also encourages the production of acid in the stomachand can cause indigestion and gastric acidity. In addition tocaffeine, tea contains tannin (which can cause constipation) and theophylline (a stimulant that increases heart rate and acts on the kidneys as a diuretic, a substance that increases the output of urine by the kidneys).

Small dosesTea and coffee have limited food value, although they do contain vitamin B and folic acid, which help prevent anemia. In small amounts, tea and coffee are unlikely to do harm.However, people suffering from indigestion, stomach ulcers, or nervousness should limit the amount they drink. In addition,people with diabetes, coronary disease, or hypertension should avoid tea and coffee.

Coffee and Tea

CAFFEINECoffee and tea are not the onlysubstances that contain caffeine.Cocoa and cola drinks that aremade from the kola nut alsocontain caffeine and relatedcompounds. If people want toavoid caffeine, they can drinkdecaffeinated coffee, herbal teas,and a whole range of caffeine-freedrinks that are now available.

Many people find that a cup of coffeehelps wake them up so that they feelready to start the day.

Is coffee really a kind ofstimulant?

Yes. Coffee has a nonspecificstimulating action on the brain.This effect is produced by theaction of caffeine, which ispresent in both coffee and tea.Many people find coffee soeffective at stimulating thearousal system that they cannot drink it in the evening,because it prevents sleep.

Q & A

SEE ALSOanemia • autonomic nervous system • blood pressure •diabetes • nervous system

NF_MC Bind_Up_pp42_83.qxd:Nutrition And Fitness 5/24/10 9:29 AM Page 51

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Most people open their bowels at regular intervals, usually onceor twice a day or perhaps once every two days. If a person’snormal pattern changes and an unusually long time betweenbowel movements is experienced, and the stools are difficult or painful to pass, then the person is suffering from constipation.As a result, the abdomen becomes swollen and the sufferer mayalso have a furred tongue with white discoloration, gas, badbreath, and even headaches.

Normally, food is moved along the intestines by regular muscleaction called peristalsis. Constipation occurs when somethinginterferes with these actions: for example, eating the wrongfoods or not enough food. Some people find they becomeconstipated if their normal routine is altered: for example, whenthey go on vacation. Lack of exercise and taking certain drugs can also cause constipation. Serious diseases such as colitis and diverticulitis can also result in constipation.

Constipation accompanied by pain on defecation tends tocreate a spiral of problems. The pain, which is commonly due to hemorrhoids (damaged veins) or cracks (fissures) in the anus,causes a reluctance to defecate. That makes the feces collect in the rectum, where more water is absorbed from them, and they become harder and even more painful to pass.

Fresh fruits, vegetables, and bran helprelieve constipation. They should beincluded in everyone’s regular diet.

Constipation

Why do I always get constipatedwhen I am on vacation?

Many people blame “vacationconstipation” on a change in the water, but it is more likely to be due to the change in yourroutine or to the stress oftraveling. Even using a strangetoilet can be a problem, especiallyif it is a different height from the one you are used to or has an unusual smell that makes you reluctant to obey your body’s command to defecate.

My father finally gave upsmoking, but now I hear himcomplaining about beingconstipated. Why would givingup smoking cause constipation?

The nicotine in tobacco smoketends to speed up the movementof food through the digestivesystem and stimulate defecation.It is the withdrawal of the drugthat has made your fatherconstipated. He should ensure hegets a high-roughage diet, plentyof fluids, and regular exercise.

Q & A


53

A badly balanced diet with too manycreamy and sugary foods such as these can cause constipation.

Constipation

CAUSES OF CONSTIPATION

Cause Additional symptoms Treatment

Persistent ignoring of signals telling the brain that the bowel is full

Persistent use of chemical laxativesthat can inhibit the colon’s naturalfunction

Muscle weakness in old age or after having a baby

Reducing food intake, anorexia nervosa,low food intake due to mental or physical illness

Obsession with bowel movements, anxiety or stress about constipation.

Damage to anus; hemorrhoids (piles)

Intestinal obstruction due to twisting or constriction of intestine

Diverticulitis (formation and inflammation of small extensions from the colon)

Headache, furred tongue, gas, badbreath, distended and possibly painfulabdomen

As above

As above

As above, plus symptoms of underlying cause of illness

May be accompanied by furredtongue, gas, and other symptomsof constipation

Painful defecation, hard bowel movements, possibly bleeding fromanus, causing tendency to “hold back’’

Vomiting, acute pain in abdomen

Pain in lower left abdomen,temperature may be raised

Try to set aside a regular time for usingthe toilet each day; increase the fibercontent of the regular diet.

Stop taking laxatives unless prescribedby a doctor; eat a high-fiber diet; drinkmore fluids; exercise more.

Change to a diet as above, but if theproblem persists, see a doctor.

If it is due to a reducing diet, take two tablespoons of bran daily (contains no calories). Otherwise, see a doctor for treatment of the underlying cause.

Try to ignore bowel movements andchange to a high-fiber diet; drink morefluids and get more exercise.

Consult a doctor, as drugs and possiblysurgery may be needed to treat theproblem, rather than self-help.

Medical emergency; get to the hospital as quickly as possible.

See a doctor as soon as possible; make a long-term change to a high-fiber diet.

TreatmentExcept when constipation is caused by a psychological or mental illness, the best treatment is common sense. Eating afiber-rich diet helps avoid or cure constipation. Fresh fruits and vegetables and cereals containing bran are excellent fibersources. Exercising also helps, because it tones the abdominalmuscles and provides relaxation from stress. Laxatives shouldnot be taken unless prescribed by a doctor. These drugs work by irritating the nerves of the intestines and speeding upperistalsis. They may cause pains and the passing of semiliquid feces.

SEE ALSOdiet • dieting • digestive system • digestive system

diseases and disorders


54

A cramp is a sudden and often severe pain, caused by thecontraction of a muscle or group of muscles. Cramps arecommon in the legs—in the muscles of the calf or in the back of the thigh. The muscles contract into a hard knot, and ordinaryefforts to move the muscles and relax them are useless. Thecramp comes on suddenly, sometimes when the person is asleep, and may last from a few seconds to several minutes.

There are various causes of cramps: for example, poorcirculation, which prevents enough blood from getting to themuscles; and sitting or lying in an uncomfortable position. Cold and exhaustion can also cause cramps. Heat can lead tosweating and the loss of salt from the body. That, in turn, leads to cramps. Another cause of cramps is unusual or hard exercise,particularly if a person has eaten immediately before exercising.It is particularly important not to eat for at least half an hourbefore swimming; cramps have caused many swimmers todrown. Some people who work with their hands, such as writers,artists, and musicians, suffer from hand cramps, and women mayhave menstrual cramps at the start of a period.

An attack of cramps can be helped by first stretching and thenmassaging the muscles. Bending the foot upward may help easethe pain of a leg cramp. Food containing salt will both preventand relieve salt-deficiency cramps. Salt tablets are available butthey can cause stomach irritation. People who suffer frompersistent cramps should check with a doctor to be sure thatthey are not a symptom of a circulatory problem.

Q & AMy brother says he suffers fromwriter’s cramp. What is it?

Writer’s cramp is also known as professional or occupationalcramp. It can affect people who use their hands for delicatework, such as musicians,seamstresses, and artists, as wellas writers. The muscles of thefingers, and even the forearm,seize, so that work with theaffected hand is impossible.

My mother is pregnant andfrequently suffers from crampsin her legs at night. Why is this?

Your mother’s muscles are underadditional strain during the day,owing to the unaccustomedweight of the developing baby.As a result, they go into spasm at night when she is lying downand relaxed. You can help her by massaging her legs when the cramp occurs, because shewill not be able to reach themcomfortably herself. Once shehas had the baby, it is likely that the attacks will disappear.

Cramps

A cramp in the calf muscle can usually be relieved by massaging the muscle,flexing the foot upward, and walkingaround for a while.

circulatory system • exercise • muscle • pain • salt

SEE ALSO


55

Diabetes mellitus is a disease in which the body does notproduce sufficient amounts of the hormone insulin. Thishormone directs the body’s sugar into the cells, where it is used as fuel. Without insulin, the cells cannot work properly.Insulin-dependent diabetes, or type 1 diabetes, is quite a common illness. It used to be fatal, but modern treatments allow diabetics (people with diabetes) to lead normal lives.

Symptoms of diabetesDiabetes can start at any age. It often begins abruptly in childrenbut progresses more gradually in adults. The body either stopsproducing insulin or makes so little that it is unable to workproperly. The most obvious symptom is a great thirst, causing people with diabetes to drink a large amount and produce a lot of urine. They also feel tired and weak because their body is not getting enough fuel. They may have blurred vision anditching skin, and because their resistance is low, they arevulnerable to all kinds of infections.

People with diabetes lose weight quickly, as their body uses up their fat as a fuel to replace sugar. This in turn producesharmful waste products that can cause a diabetic to go into a coma and to die. A doctor can easily tell when someone hasdiabetes, because the blood and urine both contain unusuallylarge amounts of sugar.

Treatment of diabetesPeople with severe diabetes treat themselves with dailyinjections of insulin. Diabetics are shown how to administer this themselves. Even young children are able to injectthemselves. Doctors figure out how much insulin each personneeds to function properly. The dose must be balanced with the person’s intake of sugar and carbohydrates, so a diabetic must eat carefully and at regular times.

Getting the balance right is extremely important; if the bloodsugar falls too low, the diabetic can go into insulin shock, knownas hypoglycemia. The patient feels hungry, then dizzy, and soonloses consciousness. Someone who feels an attack coming onshould eat something sweet as quickly as possible to raise theblood sugar. Diabetics should carry sugar lumps, candy, or othersweet foods with them at all times to counter such an attack.

People with mild diabetes may be able to control the conditionby eating carefully and keeping their weight within a reasonablerange. They must be particularly careful not to eat too muchsugar or food containing sugar. They may also need tablets to make their bodies produce more insulin.

Q & AI think my little brother eats far too much candy. All thatsugar can’t be good for him.Won’t it cause him to developdiabetes—either now or later in life?

No. If a child is going to getdiabetes, it will be the typecaused by the failure to produce insulin (a hormoneproduced in the pancreas). Being overweight or eatingsweet things has nothing to do with whether the insulin-producing cells in the pancreas are functioningproperly or not.

My father has recently beendiagnosed as having diabetes. I am afraid the illness maychange his personality, bymaking him bad-tempered, for example. Am I right to worry about this?

Not really. Obviously, diabetes,like any illness, can put thepatient under strain, but it does not cause personalitychanges. There is certainlynothing to suggest that diabeticchildren develop inadequatepersonalities because of theirdiabetes as they grow up.

Diabetes


56

Checking urine and bloodDiabetics check their urine or blood regularly to make sure thatthe sugar level is correct. The only really effective way to controlblood sugar is to check the levels in the blood at regular intervals.That is done using a small monitoring device that can determineblood sugar levels in blood taken from a small prick in the finger.Careful diabetic control reduces the risk of later complications.

Noninsulin-dependent diabetes Not all diabetics need insulin injections, but for those not taking insulin it is essential to ensure that the body’s own insulin production is adequate. Noninsulin-dependent diabetes(NIDD)—also known as type 2 diabetes or maturity-onsetdiabetes—can have serious complications. Insulin is stillproduced by the pancreas, but in quantities insufficient for the body’s overall needs.

Noninsulin-dependent diabetes usually starts between theages of 50 and 65, although it can affect people as young as 15. It may occur in people older than 65, and it may also have agenetic factor and run in families; of every three people withNIDD, approximately one has a relative who is also affected withthe disorder. This type of diabetes usually starts with insulinresistance, a condition in which the cells cannot use insulinproperly. At first, more insulin is made to compensate, buteventually the pancreas loses the ability to secrete insulin.

A principal, but not the sole, cause of NIDD is obesity. About 80 percent of people with NIDD are obese. For reasons that arenot fully understood, obesity is associated with a state known as insulin resistance. It may simply be that the number of insulinreceptor sites is inadequate, or it may be that the mechanismstriggered in the cell by insulin locking are adversely affected. It is known that people in wealthier societies tend to eat morefood, which leads to a rise in obesity and hence a rise in NIDD.

Controlling NIDDThe object of treatment is to keep blood sugar levels withinnormal limits so that complications do not occur. Exercise and a healthy diet to maintain an appropriate weight are importantin controlling blood sugar levels. In many cases, NIDD can becompletely controlled by diet alone. What is eaten is just asimportant as how much is eaten. The aim is to control the bloodsugar without drugs, but if necessary, production of insulin can be boosted by sulfonylurea drugs such as tolbutamide,chlorpropamide, or other drugs. If these drugs fail, insulininjections will then become necessary.

Diabetes

CAUTIONDiabetics can lead a comparativelynormal life. However, they shouldwatch what they eat and talk to a doctor about vigorous exercise,which uses up blood sugar quickly.Diabetics need regular checkupsand should always tell a dentist ordoctor about their condition beforeundergoing any kind of treatment.When someone has had diabetesfor a number of years, it can causeproblems in other body systems.The eyes, nervous system, kidneys,and arterial system can be affected.Since diabetics may have poorcirculation, they should always takeparticularly good care of their feet.

It is a good idea for people with diabetesto wear a tag such as this. If they were toslip into a diabetic coma, the emergencymedical service would know immediatelythat they were diabetic, and precioustime would be saved.


57

Diabetes

Right: If no insulin is produced by thepancreas, glucose cannot be stored in the liver or used by the cells. Instead, thecells produce energy by burning up fats;fats cannot be burned properly withoutglucose and therefore they produce ahigh acid level in the blood. Unless thisproblem is treated, the toxic acid level will affect the brain, and the diabetic will go into a coma.

Left: Insulin, made by the pancreas, allowsglucose, which body cells must burn to produceenergy, to be stored in the liver. When the bodycells need more energy, and therefore moreglucose, this glucose is released, and the insulinenables it to be used by the cells.

INSULIN WORKING NORMALLY

HOW LACK OF INSULIN CAUSESA DIABETIC COMA

body tissue

pancreas

liver

brain

liver

pancreas

body tissue

Insulin GlucoseAcid

SEE ALSOcarbohydrates • circulatory system • diet • obesity •sugars • tiredness


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The body is like an engine, and food is the fuel it needs to keeprunning. How efficiently the body works depends on what isconsumed. The food a person eats is changed into energy andused by the body for different functions, such as walking andrunning and the constant process of growth and repair of thebody tissues. The amount of energy (and therefore the amountof food) needed depends on how much energy is used; on thetype of activities performed; and on body size, sex, age, andgeneral health. Figures given for the needs of a person at rest are known as the basal metabolic rate. Every person must eat the right amount of food to fuel his or her needs. If more food is eaten than is needed, the excess is stored as fat and the person becomes overweight.

Carbohydrates, proteins, and fatsFood can be divided into three main types: carbohydrates,proteins, and fats. Carbohydrates are present in starch (potatoes,bread, yams, peas, corn, beans) and sugar (fruit, honey, tablesugar). Sugar-rich foods include jams, cookies, chocolate, candy,and ice cream. Meat, fish, eggs, cheese, milk, soybeans, nuts, some pulses, lentils, and seeds are rich sources of protein.Carbohydrates and fats are used to fuel the body’s processes and functions; protein is used as building material for the tissues,including muscles and bones. Fats provide nearly three times asmuch energy as other foods, so fewer of them are needed in thediet. In the West, people eat far too much fat. About 40 percentof their energy comes from fats, and this situation has led tohigh levels of obesity and diseases of the arteries and the heart.

Vitamins, minerals, and roughageThe body needs vitamins A, B, C, D, E, and K and minerals such as calcium, phosphorus, iron, iodine, potassium, magnesium,fluorine, zinc, and copper. Vitamins are essential for normalgrowth and development, and because they cannot be made by the body, they must be included in the diet. Vitamins can betaken as supplements. Minerals assist in many of the processesneeded for normal nerve and muscle function and must besupplied frequently in the diet.

Roughage, or dietary fiber, consists of the walls of plant cellsthat cannot be broken down by digestion and therefore passthrough the stomach and intestine in solid form. Roughagestimulates the action of the intestine and enables food to passthrough the digestive system more easily. It also provides thebulk to make feces solid. The best-known example of roughage is bran. Vegetables, nuts, and cereals also contain fiber.

Q & AI want to become a vegetarian,but my friends say I won’t getenough protein if I don’t eatmeat. Is this true?

It is perfectly possible to supplyall the body’s needs withouteating meat, but you will need tomake some adjustments to yourdiet. For example, some of yourprotein will have to be providedby nuts, beans, and cereals.

Diet

MACROBIOTICS

Macrobiotics is an Eastern theory of diet based on the belief thatpeople are what they eat and thatfood not only affects health butalso influences how people feel,think, and behave. The macrobioticdiet relies on a balance betweenthe yin (female) and yang (male)qualities of food. Few fresh fruitsand salads are eaten. Foods derivedfrom animal products, such asmeat, butter, eggs, and milk, are not allowed. Essential foods in thediet are brown rice, dried beans,and other whole grains. Miso, a paste made from fermentedsoybeans, adds flavor to food. The macrobiotic diet is not suitablefor children or growing adolescents.


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Diet

The original food guide pyramidemphasized the importance of eatingmore foods in the blue and yellow bandsand fewer in the green and red bands.

fats andsugars

dairyfoods

grainfoods

proteins

fruits andvegetables

The five food groups in the MyPyramiddiet are grains (orange band), half ofwhich should be whole grains; vegetables(green band); fruits (red band), which canbe fresh, canned, frozen, or dried; milkproducts (blue band), preferably low-fator fat-free; and meat and beans (purpleband), mainly lean meat and poultry, fish,beans, nuts, and seeds. The wider theband, the more that food should be eatendaily. The narrow yellow band representsoils (fats), which should be eatensparingly. Experts recommend that a dietshould be low in fats, cholesterol, salt, andadded sugars. One of the aims of thispyramid is to highlight the vital healthbenefits of making small, simpleimprovements in nutrition, physicalactivity, and lifestyle behavior.

basal metabolism • carbohydrates • dieting • fats •food and nutrition • health foods • obesity • protein

• sugars • vitamins • weight control

SEE ALSO

STEPS TO A HEALTHIER YOU

A balanced diet and food pyramidsA balanced diet supplies all the necessary nutrients in quantities that suit a particular individual. The original food guide pyramidrecommended that people should eat plenty of whole-grainfoods, vegetables, and fruits and fewer high-fat, high-sugar foods.In 2005, the United States Department of Agriculture (USDA)updated the old food pyramid and put forward new guidance in the form of “MyPyramid: Steps to a Healthier You.” This systemwas designed to help people make healthier food choices and to be active every day.

The old food pyramid has been turned on its side so that allthe food group bands now run from the top of the pyramid tothe base. The different size of each band shows the proportionfrom each food group that should be eaten each day. The widerthe band at the base, the more of that food should be eatenevery day. The emphasis is on a high-fiber, low-fat diet.

The steps at the side of the new pyramid are to encouragepeople to be active every day. There are 12 different pyramids tochoose from, depending on how many calories a person needsand how active he or she is. This emphasizes the need for a morepersonal and individualized approach to improving diet andlifestyle. One pyramid is aimed at children to help show them theimportance of healthy eating and physical activity and to addressthe very serious problem of childhood obesity.

grains

oils milk products meat and beans

vegetables fruits


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The most common reason for dieting is being overweight. Peopleput on excess weight because they are taking in more energy(calories) in their food than they are using. Obesity—being more than 30 percent above the ideal body weight—is reachingepidemic proportions in the United States and in other developedcountries. Obesity is a serious risk to health; it can lead to heartdisease, high blood pressure, and diabetes.

There are no hard-and-fast rules about how much peopleshould eat and drink. Some people can consume what they likeand still stay slim; other people gain weight on an apparentlynormal diet. The difference happens because the rate at which a person’s body uses energy—the metabolic rate—varies fromone individual to another.

Healthy choices and exercisePeople who want to lose weight need to cut down on theamount they eat, but they should still eat a balanced diet that includes lean meat, poultry, fish, fresh fruits and vegetables,whole-grain bread, brown rice, and low-fat milk products, such as spreads and cheeses. They should also avoid or cut downdrastically on food containing a high proportion of sugar and fat, such as cookies, candy, cake, french fries, hamburgers, salami,and fried food. Neither should they eat too much protein

Q & AI want to lose weight, but I’mconfused by all the differentdiets and their claims. I amlooking for a simple andeffective way to lose weight.What should I do?

A reducing diet allows for around 1,000 calories a day. It should include a variety offoods low in fat and plenty of cooked or raw vegetables,fresh fruits, meats, and grainproducts. Try to avoid using salt and excess sugar.

I’ve decided that I need to go on a diet. Can I still eat as muchas I want of foods that areadvertised as being “low-fat”? If not, why?

No. Even if a product isadvertised as having zero fat, it can still contain lots ofcalories. In fact, in a product that is fat-free, manufacturershave often replaced the fat with sugar. Always check thefood’s calorie content on thenutrition label.

Dieting

Eating plenty of fresh fruits andvegetables and drinking water ratherthan sweet drinks or alcohol keeps these two women slim and healthy.


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containing saturated fat, because that increases the body’sproduction of unhealthy cholesterol. Dry beans, peas, and lentils are good sources of low-fat vegetable protein, and when combined with grains, these pulses make a good meatsubstitute. The MyPyramid food guidance system put forward in 2005 by the United States Department of Agriculture (USDA)is designed to help people make healthier food choices andemphasizes the importance of physical activity in keeping one’s weight at a healthy level.

People who are dieting should not cut out meals completely. If they try to get through the day without eating, they will findthemselves filling up later with junk food. They should eat threesmall meals a day and cut out sugary snacks. If they must eatbetween meals, they should nibble a celery stick or an apple.

Eating too much salt is bad because it makes the body retainmore fluid. Cutting down on salt allows the body to eliminatefluid, and this loss of fluid makes a person slimmer. It is best not to cut down on the amount of liquid consumed; drinking less has no effect on weight. The only liquids that should be cut out are sweet drinks and alcohol; drinks containing caffeineshould be limited.

Permanent changesOne of the keys to successful dieting is a genuine desire to loseweight. The type of diet that is followed is also an importantfactor. All kinds of diets come into and out of fashion. Some dietssuggest that only one type of food, for example bananas, shouldbe eaten for several days; others rely on special packaged dietmeals that claim to contain all the nourishment needed. Neithertype of diet, however, is likely to provide sufficient nutrients.Many people go on crash diets and lose several pounds quickly.Dieting, however, is not just a matter of losing weight. It alsoinvolves not putting weight on again. Many dieters lose weighton a crash diet and then go back to their old eating habits. Before long, they put all the weight back on.

The best way to lose weight is not to diet at all but to changeeating habits permanently. By eating sensibly and altering theproportions of the foods that are eaten each day, a person shouldbe able to lose 1 pound (450 g) a week. In six months, that willequal a weight loss of about 25 pounds (11 kg). This weight losscan be achieved on a diet that is interesting, is balanced, and

Dieting

Foods such as hamburgers and fries are popular, but they should beavoided or eaten sparingly, because they contain extremely high levels of fats and sugar. Consequently, their calorie content is very high.

CUT DOWN ON

• Butter, cream, and ice cream• High-calorie cheese• Fatty meats such as bacon,

hamburgers, and salami• Fried foods• Desserts, cakes, cookies, and pies• Chocolate and candy• Dried nuts• Thick sauces• Sweet drinks

INSTEAD EAT

• Whole wheat bread• Brown rice• Pasta • Vegetables• Fruit • Skim milk• Lean beef, lamb, and pork• Chicken and turkey• Dry beans• Whitefish


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does not leave the person feeling hungry. Such a dieting methoddoes not mean eating different food from other people. It meansavoiding certain foods; eating less of some, more of others; andgenerally eating slightly less.

Weight-loss groups and counselingMany people find it helpful to join a weight-loss group in whichdieters encourage one another and exchange helpful tips. Theycan discuss their problems, work out a sensible diet that suitseach invidual, and have fun exercising with friends. If someonefinds losing weight difficult, he or she should consult a counselorwho will be able to advise and help. If someone falls short of aweight-loss target, he or she should not be discouraged but keeptrying. When people have lost as much weight as they want, theycan keep their weight at the new level by continuing to eat abalanced diet, joining in sports activities, and exercising regularly.

As people lose weight, they should check themselves regularlyonce a week against weight-for-height charts. They shouldensure that they do not fall below the ideal weight range. Beingtoo thin is as undesirable as being too fat and is also unhealthy.People who are worried about being too heavy or too thin shouldtalk to a counselor, teacher, or doctor.

Dieting

SPECIAL DIETS

Doctors prescribe special diets as part of the treatment for somediseases, such as liver and kidneydisorders, hypertension (high blood pressure), gastrointestinaldisturbances, and diabetes.

Kidney and liver illnesses may betreated with a protein-free diet,consisting largely of bland, sweetpuddings and unsalted butter. This is a short-term diet, however,to be used in emergencies only.

Patients with hypertension areoften put on a low-salt, low-cholesterol diet, which reduces or cuts out all animal fats, dairyproducts, eggs, and candy.

Gastrointestinal disturbances aremade worse by any diet containingtoo much fiber, so people withsevere cases should avoid high-fiberfoods, such as whole-wheat breadsand cereals, nuts and legumes(peas, beans), and most raw fruitsand vegetables.

Diabetics must keep strictly to adiet that contains fixed amounts ofcalories and carbohydrates; unlessthey adhere to this, they may loseconsciousness and go into a coma.

A fruit smoothie, such as this bananasmoothie, is a healthy snack that is low in calories, sugar, and fat. It contains only nonfat yogurt, a banana, crushed ice, and a little honey.

anorexia and bulimia • basal metabolism • diabetes •diet • exercise • food and nutrition • food labeling •obesity • weight control

SEE ALSO


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The digestive system is the part of the body that breaks downfood into a form that can be absorbed by the cells. The digestivetract is sometimes called the alimentary canal. It consists of themouth, throat, esophagus, stomach, and intestines.

From mouth to stomachIn the digestive system, digestive juices called enzymes act on the food that is eaten. Organs connected with the digestivetract produce these enzymes. Digestion begins in the mouth. As food is chewed, glands beneath the tongue increase theproduction of saliva, which contains the enzyme ptyalin. Thisenzyme starts breaking down some of the carbohydrates in the food into glucose and maltose, which are simple sugars.

From the mouth, the food travels through the throat anddown the esophagus, or gullet. There, the gastric juices—amixture of secretions composed of mucus, hydrochloric acid, andanother enzyme, pepsin—are mixed with the food. The gastricjuices in the stomach start to work on the proteins (foods suchas eggs, cheese, chicken, and meat). The muscles in the walls of the stomach knead and churn the food around to aid digestion.

The small intestine, pancreas, and gallbladderAbout four and a half hours after swallowing food, the partiallydigested mixture leaves the stomach in the form of a thickish,acidic liquid called chyme. This liquid passes into the duodenum,the first part of the small intestine, which is a coiled tube about20 feet (6 m) long. The duodenum is the first part of the smallintestine, which is about 10 inches (25 cm) long. Chyme containsa quantity of acid and enzymes that could damage the duodenum,but the duodenum plays a vital part in digestion by making andreleasing large quantities of mucus, which protect the lining. Thealkaline duodenal juices are produced under the influence of thehormone secretin, which helps neutralize the acids in the chyme.

The pancreas and the gallbladder also help with digestion. In response to the presence of food in the upper digestive tract,the gallbladder adds more enzymes that break down fats, nucleicacids, proteins, and carbohydrates. Bile is released via the bileducts from the gallbladder, where it is stored. Bile is a yellowishfluid secreted by the liver, which helps digest fats.

From the duodenum, the partially digested food passes intothe rest of the small intestine. The food takes nearly three hoursto pass through the long, narrow tube of the small intestine.During its passage, the food is broken down completely by aseries of enzymes. Amylase converts starch into maltose; lipaseconverts fats into glycerin and fatty acids; and trypsin reduces

Q & AIs it true that babies can’t digest cow’s milk?

Compared with human breastmilk, cow’s milk contains large amounts of a protein called casein, which babies do not have the equipment to digest properly. The manypowdered formula milks forbabies are made from cow’s milk and thus contain morecasein than breast milk, but the formula milks are speciallytreated to make the casein more digestible. However, breast-feeding is better for a baby’s digestive system, and in other ways, too.

My three-year-old sister lovesspicy foods. However, won’t they upset her stomach and her digestion?

There is no reason why spicyfoods should cause her anyproblems. By the age of three, a child’s digestive system cancope with an extremely mixeddiet, and the degree of toleranceto spicy foods will vary, just as it does in adults. As long as thesefoods do not give her diarrhea or make her vomit, let her have foods that she likes.

DigestiveSystem


64

proteins to amino acids. More enzymes are released from thewalls of the small intestine to complete digestion. The broken-down food is now ready to be absorbed into the bloodstream.

Absorbing nutrientsThe lining of the small intestine contains millions of minuteprojections called villi. Each villus is covered by a cell layer thatabsorbs nutrients. These cells have projections called microvilli.Both the villi and the microvilli increase the surface area of thesmall intestine to enable the efficient absorption of nutrients.The central core of each villus contains a capillary (a small bloodvessel) and lacteals, which are branches of the lymphatic system.This system is a network of tiny tubes (the lymph vessels)carrying lymph, which is normally a colorless fluid. After a fatty meal, the lymph in the lacteals is milky white, owing to the presence of tiny fat globules. The function of the lymphaticsystem is to return liquid to the bloodstream. When digestedfood comes into contact with the villi, the glycerols, fatty acids,and dissolved vitamins enter the lacteals and travel through the lymphatic system to enter the bloodstream.

Other substances are absorbed directly into the capillaries in the villi. These substances include amino acids from proteindigestion; sugars from carbohydrates; vitamins; and importantminerals such as calcium, iodine, and iron. From the capillaries,these substances go to the liver, which extracts some of them.The rest go into the general blood circulation and are taken to the cells to provide them with energy.

The large intestineWhen the digested food has gone through the small intestine,the remainder passes into the large intestine, or colon, as waste.The colon extracts water from the waste, which collects in therectum and passes out through the anus as feces.

Digestive System

Partially digested food (chyme) is movedthrough the intestine in waves, as thewalls of the intestine contract and thenrelax. This wave movement is calledperistalsis. It is stimulated by the presence of food in the esophagus.

The surface of the small intestine iscovered with small, fingerlike projectionscalled villi. They increase the surface areaand allow food to be absorbed quicklyinto the capillaries (blood vessels).

capillaries

villi

chymestimulatingwave ofperistalsis

chyme

lymphvessels


65

Digestive System

MOUTH Food is taken into the mouth.

SALIVARY GLANDS They produce saliva, which moistens the food while the enzymes it contains start digestion.

ESOPHAGUS Waves of muscle action calledperistalsis move the food down theesophagus, or gullet, and into the stomach.

STOMACH In the stomach, the food is mixedwith digestive juices. After two to six hours,it is converted to a liquid called chyme.

SMALL INTESTINE Waves of peristalsis pushchyme through the stomach and out insmall amounts into the small intestine. The small intestine of an adult measuresapproximately 20 feet (6 m) long and 1.5 inches (4 cm) wide. Most of the digestiveprocess happens here.

LIVER AND PANCREAS The liver and pancreasproduce digestive juices.

LARGE INTESTINE Chyme passes from the small intestine into the large intestine,which is about 3 inches (7.5 cm) in diameterand 3 feet (1 m) long. The appendix leads offthe large intestine.

COLON The greater part of the largeintestine is known as the colon. As chymepasses through the colon, water is absorbedinto the blood.

RECTUM In the rectum, only solid fecesremain. They are pushed out through theanus by deliberate muscle contractions.

mouth

salivary glands

DIGESTIVE SYSTEM

esophagus

stomach

liver

pancreas

smallintestine

largeintestine(colon)

gallbladder

duodenum

appendix anus

rectum

SEE ALSOdigestive system diseases and disorders


66

Many digestive disorders are caused by the food people eat. The digestive system works best when people eat a dietcontaining a good deal of fiber and not too much fat. A low-fiber diet can cause constipation (infrequent bowel movements,with small, hard stools), and eating extremely spicy food cancause diarrhea, if people are not accustomed to such food.

Indigestion, or dyspepsia, can be caused by nervousness, eating too fast, and emotional stress. It results in discomfort,belching, and heartburn. Also associated with indigestion isflatulence, which is a buildup of gas in the intestines. Sensibleeating habits and relaxation are the most common treatmentsfor indigestion.

Contaminated food and appendicitisSome painful and dangerous illnesses are caused by eating foodcontaminated by bacteria, including staphylococcal poisoning,salmonella poisoning, amebic and bacillary dysentery, botulism,cholera, and typhoid fever. These illnesses cause many symptoms,inlcuding vomiting, abdominal pain, and diarrhea. Foods may be contaminated by chemicals, which cause vomiting, or bepoisonous themselves, as are some fungi.

Appendicitis is inflammation of the appendix, normally as a result of bacterial infection. It is most common between theages of 15 and 24 years. The symptoms include pain in the lowerright abdomen and sometimes nausea and vomiting. Treatmentinvolves surgery to remove the appendix.

Ulcers and inflammationUlcers are small, open sores that form when the mucousmembrane lining the digestive tract is damaged. Small ulcersoften form in the mouth but heal quickly. Ulcers in the stomachand duodenum are more serious. Although the exact cause is unclear, the bacterium Helicobacter pylori may causeinflammation and ulceration by increasing stomach acid. Ulcers are more common in people who eat hurried and irregular meals, who drink heavily, who smoke, or who arenervous and under stress.

Inflammation, thickening, and ulceration of the colon oranother region of the digestive tract can cause Crohn’s disease,with cramps and pains after eating. There may be persistentdiarrhea, abdominal pain, fever, loss of weight, and bleeding,leading to anemia. Drugs can relieve the anemia, but surgerymay be needed. Inflammations and ulcerations of the colon arecalled colitis. Some inflammations are caused by an infection or an allergy and last a short time, but others are chronic

Q & AMy mother says that laxativesare dangerous and that youshould always treat constipationnaturally. Is she right, and whatdoes she mean by “naturally”?

Yes, your mother is right. Too many laxatives can harmyour digestive system. The best natural remedies forconstipation are bran, freshfruits, and vegetables. Thesefoods contain the naturallyoccurring substances, especiallyfiber, that encourage the bowels to move regularly, withoutharming them.

My grandmother got very sickwhen she was at our house andshe had symptoms of diarrhea.However, when the doctor came, he said it was reallyconstipation. How could this be?

This is a rather common ailmentin the elderly, called spuriousdiarrhea. The lower intestinegets clogged with feces, yetsome liquid matter manages toget past the blockage, appearingas diarrhea, and may cause theolder person to lose control of the bowels and becomeincontinent. However, thisproblem can be easily treated.

DigestiveSystem Diseasesand Disorders


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Digestive System Diseases and Disorders

GASTROINTESTINAL DISORDERS

Bad breath (halitosis): Unpleasant odordue to swallowed food or drink, dentaldisease, or sometimes disorders of therespiratory or digestive systems

Foreign bodies: Fish bones, toothpicks,buttons, coins, and so on, swallowed by children and the unwary

Gastritis: Inflammation of the stomachlining, caused by drugs, food poisoning,infection, alcohol, or eating the wrongtype of food (acute); inflammation of the lining of the stomach, leading toulceration and hemorrhage, caused by poor diet, alcoholism, enzymedeficiency, hiatus hernia, diabetes,cancer, or emotional stress (chronic)

Gastroenteritis: Inflammation of thelining of the stomach and the intestines

Hemorrhoids (piles): Swollen andtwisted veins that are located in theanal canal, hemorrhoids may becomeulcerated or thrombosed and mayeventually protrude from the anus; they occur in most adults.

Infection and infestation: Bacteria,viruses, and various types of parasitesmay live in the human digestive tractover a period of time and cause a variety of problems.

Malabsorption: Failure of absorption of nutrients from the digestive tract due to various disorders

Nausea and vomiting: Vomiting isusually a natural response to harmfulsubstances that must be expelledundigested from the body. Some feelings of nausea and vomiting are psychological in origin.

Peritonitis: Inflammation of the lining of the abdominal cavity and the organs(peritoneum), which is most commonlycaused by the perforation or the ruptureof an organ such as the appendix, or perforation of an ulcer

Polyps and benign tumors: A growth of protruding tissue that can ariseanywhere in the digestive tract

Bad breath

Choking, or severe pain in colon

Pain in abdomen, loss of appetite,nausea, vomiting, and diarrhea (acutegastritis); pain on eating, pain in back,rapid feeling of fullness, nausea, andblood in vomit (chronic gastritis)

Pain in abdomen, loss of appetite,nausea, vomiting, and diarrhea

Pain and bleeding during defecation,constipation

Various

Weight loss, increased excretion ofprotein and fat, diarrhea, and anemia

Nausea due to real or imagined cause;deliberate vomiting during tempertantrums, or on eating wholesome but unpalatable food, or because of an eating disorder

Mostly sudden, severe, localized pain in the abdomen, spreading, and leadingto shock

Bleeding, cramps, abdominal pains, or no symptoms

Removal of cause, change of diet, and good dental hygiene

Small round objects can pass throughthe digestive tract with no problem.Sharper ones may require surgery.

Usually corrects itself when the causehas been eliminated by vomiting ordiarrhea; bed rest and bland diet arerecommended (acute). Treatment forspecific diseases and avoidance ofalcohol, tobacco, and very spicy food;bland diet with small meals eatenfrequently; removal of causes of stress,or prescription of tranquilizers (chronic)

As for acute gastritis (above)

May regress naturally with high-fiberdiet; hemorrhoids may be injected, or removed surgically.

Various

Various specific diets and treatments

Treatment of physical disorder, if present; reassurance andpsychotherapy if not

Emergency operation, or occasionallymedication

Polyps should be removed by surgery,because some do become cancerous.

Disorder Symptoms Treatment


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conditions. Symptoms are abdominal pain and diarrhea. Chroniccolitis may never clear up completely.

One problem of the large intestine is irritable bowel syndrome.Its cause is not really known, but attacks may be triggered bystress. The main symptoms are spasmodic lower abdominal pain and bouts of diarrhea and constipation. A high-fiber dietand antispasmodic drugs may help, but people with irritablebowel syndrome may find it recurs after long gaps, usually when they are nervous or under stress.

Hernias and diverticular diseaseThe lining of the esophagus is seldom damaged. Sometimes,however, a hiatal hernia forms at the point where the esophaguspasses through a gap in the diaphragm and into the abdomen.Part of the esophagus and the upper stomach then bulges back into the chest, and acid from the stomach may make its way back into the esophagus, causing a burning sensation calledheartburn. The lining of the esophagus can also be damaged by swallowing acid or a strong alkali.

Sometimes, bulges called diverticula form in the colon, whichis the major part of the large intestine. These bulges developwith age, and waste matter may fill them and become infected,causing diverticulitis. The condition can cause bleeding.Alternatively, an inflamed diverticulum may bulge into theabdominal cavity. This extremely serious condition needsimmediate surgical treatment. However, rest, a healthy diet, and antibiotics help control diverticulitis.

Cancer of the digestive systemCancer is unusual in the small intestine but common in thestomach and colon. Treatment may include a combination of surgery, radiotherapy, and chemotherapy. If the disease is diagnosed and treated early enough, patients can live a normal life.

The symptoms are similar for mild or serious cases, so people should consult a doctor if they have long-lasting pain or nausea, if they lose their appetite for more than a few days, if their normal pattern of bowel movements changes, or if theyhave bleeding.

Digestive System Diseases and Disorders

Irritable bowel syndrome results inspasmodic lower abdominal pain andbouts of diarrhea and constipation. Stress and nervousness make it worse.

SEE ALSO

digestive system • food poisoning • hernia • indigestion

• irritable bowel syndrome • pain


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A great many people suffer from physical or mental disabilities,or from a combination of both. Sometimes, these disabilities arecaused by an inherited condition or by damage at birth. Otherdisabilities are the result of accidents. A disability may or may not be a handicap; if a disability interferes with a person’scapacity to fulfill his or her expectations in life, it is described as a handicap. For example, a ballet dancer is more likely to be handicapped by a limp than a computer operator is.

Born with a disabilityParents of a baby with a disability need help from the verybeginning to enable them to come to terms with the problemand to ensure that their baby gets the best possible treatment.There are many voluntary organizations that provide help andadvice, and public help may be available as well. There is often a great deal that parents themselves can do to help their child,such as carrying out special exercises and structured playactivities. As the child grows up, special schooling may benecessary, either locally, if available, or in a residential center.

Illness and accidentsIf people become disabled later in life as the result of an illness or an accident, treatment is based on helping them to do asmuch as possible for themselves. When possible, disabled peopleare encouraged to take up sports, which help them improve theirphysical condition and provide stimulation, self-respect, andfulfillment. It is particularly important that people who areimmobile look after their health, as they are often at risk ofinfection and problemssuch as pressure sores.People without feeling in a body part are also at risk, because they mayhurt themselves badlywithout realizing it.

Disability aidsAll kinds of aids have been developed to make it easier for people with

Q & AMy brother has been severelydisabled by a car accident and is now confined to awheelchair. He used to beenthusiastic about sports. How can he continue thisinterest from a wheelchair?

There are many athleticopportunities for the disabled,such as archery and golf, and many people take part in wheelchair sporting events.You should contact your localassociation for the disabled,which will be able to give you more information. You can get the address from your public library.

My four-year-old sister isphysically challenged and needs my parents a lot. She has to go to the hospital, and I am worried that she won’tmanage on her own. What can my parents do?

Many hospitals encourageparents to stay in the hospitalwith their young children. If this is not possible in yoursister’s case, your parents canvisit regularly and explain your sister’s likes, dislikes, and needs to the hospital staff.

Disabilities

Many people in wheelchairstake up competitive sports,which strengthen theirremaining working muscles.


70

disabilities to lead an independent life. Wheelchairs are constantlybeing improved and made easier to maneuver, and increasingnumbers of stores, hotels, theaters, and offices are designed to give ease of access to wheelchair users. There are also devicessuch as easy-to-grip faucet handles and computers that enableseverely handicapped people to type, answer the telephone, and turn switches on and off, even if the only movement thatthey are capable of is sucking or blowing through a tube.

Microprocessor technology has been applied to the design of bionic parts, such as arms. These artificial body parts can be activated by tiny electrical signals that originate from thedisabled person’s own nervous system, so that he or she canperform virtually normal actions.

Elderly people make up the greatest number of the disabled.Most of the effort in treating them medically is devoted topreventing the progress of a disease when possible andalleviating any social and physical distress.

Disabilities

This diagram shows how an artificial limb works. Thewearer can work the elbowjoint and hand by moving the stump of his or her arm,the shoulder blades, and theback. The red arrows indicate the movements that can beachieved by using the harnessand moving the stump of the limb. The blue arrowsindicate the adjustments that are possible by using the other hand.

muscle • nervous system • paraplegia • stroke

SEE ALSO


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The body weight is about two-thirds water. Water is essential to enable the body’s delicate chemical processes to take place. An adult loses around 4 pints (1.9 l) of water every day in breath,feces, sweat, and urine. Part of that water is replaced in food(which is 70 percent water); the rest is replaced by drinking.People are unlikely to live for more than a few days if they havenothing at all to eat or drink, but they can survive for about twomonths without food if they have enough to drink.

The only fluid needed is water; most people take it in the formof drinks such as coffee, milk, soft drinks, or tea. In hot weather,people need to drink more than usual. However, it can beharmful to drink too much water. A healthy body carefullyregulates its water content. People experience thirst when the body needs water. Excess water is excreted in the urine.

If the body loses too much water, dehydration occurs. Thesymptoms include dry skin, weakening muscles, kidney problems,disorientation, and hallucinations. When people have a fever, they perspire more and often eat less. As a result, they maybecome dehydrated, especially if they vomit and have diarrhea.Those with a fever or upset stomach need to drink lots of fluids.

In some parts of the world, drinking water supplies may carry serious diseases, including cholera and typhoid fever.

Q & AIs it safe to drink water directlyfrom a faucet?

In many parts of the world,especially in developingcountries, faucet water is notsterilized and may containbacteria that can cause serioushealth problems. In the UnitedStates, Canada, and many othercountries, drinking water ischlorinated, so such healththreats are likely to have beeneradicated. Other problems may occur if you ingest toomuch lead from water in oldpipes or faucets (faucets madeafter 1997 contain less lead). If you are in any doubt, youshould run the water for oneminute before using it, use coldwater for cooking, and drinkbottled water instead.

I’ve heard that asbestos cancause some types of cancer. Is there any risk of this fromdrinking water that has passedthrough cement-impregnatedasbestos pipes?

No. Surveys of areas where thesetypes of pipes have been in usefor many years show that thereis no increased risk of cancers of the bowel or abdomen.

Drinking Water

During performance and training, athletes lose a great deal of body fluidthrough sweating. To avoid dehydration, they need to drink lots of liquids.

coffee and tea • muscle • skin • sweat

SEE ALSO


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The elbow is one of the most important joints in the body. Threemain bones meet there: the radius and the ulna (which are thetwo bones of the forearm) and the humerus (which is the singlelong bone in the upper arm). The elbow is a double joint. Thehumerus and the ulna (the longer of the forearm bones) arelinked with a hinge joint, which enables the arm to bend up anddown. The humerus and the radius are linked with a ball-and-socket joint, which enables the arm to be twisted to and fro and the position of the hand to be changed.

The ends of each of the bones in the elbow are covered with a smooth cartilage, which provides a low-friction surface. Theelbow joints are lubricated with a clear liquid called synovialfluid. The muscles that control elbow movement are linked to thebones by tough tendons. Bursae, little pouches filled with fluid,lie between the tendons and bones; they also prevent friction.

The most common wear-and-tear injury is bursitis, in which a bursa becomes swollen and inflamed. This problem is usuallycaused by injury or pressure but may also be due to a bacterialinfection. The treatment includes rest or, if the cause is infection,antibiotics. Another common complaint is tendinitis, orinflammation of the tendons. The condition is called tenniselbow when tendons on the outside of the elbow are affectedand golfer’s elbow when the tendons on the inside are inflamed.Again, rest is the main treatment required.

Q & AI get an odd sensation in myelbow when I bang my funnybone. What causes such astrange feeling in this bone?

One of the nerves of the arm, the ulna nerve, lies in a groove ofbone near the tip of the elbow.When the elbow is hit, the nervebecomes pinched in the groove,generating the tingling, painfulsensation that gives the funnybone its name.

I injured my right shoulderrecently, and now I am havingsome difficulty moving my rightelbow. Why would a shoulderinjury affect my elbow?

Many of the elbow’s movementsdepend on the actions ofmuscles that are attached at oneend to the shoulder and at theother end to the bones of theforearm. Because these musclesare involved in elbow movement,any injury to the shoulder canalso affect the elbow.

SEE ALSOfractures and dislocations • joints • ligaments •shoulder • sports injuries • tennis elbow

Elbow

The humerus, ulna, and radius meet at the two joints that form the elbow (1). Thebiceps muscle runs from the shoulder tothe top of the radius; the triceps runs fromthe shoulder to the humerus and ulna (2).

ballandsocketjoint

radius

ulna

radius

bicepscontracts to raiselower arm

triceps relaxes

humerusscapula (shoulder blade)

hingejoint

12

ulna


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Swimming (above) is an excellent form of aerobic exercise for improvingall-around fitness. Because the body is supported in the water, there is lesslikelihood that soft tissues will be overstrained. Running (left) is a weight-bearing exercise that can help to increase bone strength. Correcttechniques should be used, and suitable shoes should be worn, tominimize wear and tear on joints.

The human body is a living machine, and it needs to exercise tostay in good shape. Regular physical activity works the musclesto keep them strong and boosts the immune system. Exercisekeeps the heart and lungs in good working order so these vitalorgans can better supply the body with oxygen. Regular exercisereduces the risk of heart disease, high blood pressure, insomnia,and diabetes. Exercise also speeds up the metabolism, makingthe body release fat stores as a source of energy. This increase inmetabolism encourages weight loss and helps prevent obesity.There is also the feel-good factor: exercise is known to improvemental health and prevent depression.

Different types of exercisesSustained exercise that makes people breathless and sweaty iscalled aerobic exercise. This form of exercise promotes generalphysical fitness and a sense of well-being. Aerobic exercise worksthe heart, lungs, and muscles and increases blood flow throughsoft tissues. Cycling, running, jogging, swimming, walking, andsports such as rugby and tennis are excellent forms of aerobicexercise. Anaerobic exercise develops muscle strength and power.Weight lifting is perhaps the most familiar form of anaerobicexercise. It involves tensing muscle groups by pulling or pushingagainst a set of weights. Sprinting is another form of anaerobicexercise that increases short-term muscle strength.

Q & AMy mother won’t let me goswimming right after I’ve had a light meal. She says I’ll getstomach cramps if I do. Why?

After eating, the stomach andintestines need extra blood toaid digestion. The muscles alsoneed more blood for swimming.If they do not receive enough,they are deprived of oxygen andgo into spasms. Therefore, it isbest to take a half-hour rest aftera light meal so that the stomachcan empty itself.

Exercise


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Before high-impact exercise, such as ballsports, people should take time to warmup correctly. Injury is less likely to occurwhen muscles have been prepared bypreliminary stretching exercises.

Flexibility exercises are animportant part of any exerciseprogram. They improve the range of movement of muscles and joints.Yoga is a good example. It includesexercises to tone muscles, tendons,and ligaments and improvecirculation. Yoga includes deepbreathing, which helps relax the body and mind.

Amount of exerciseThe amount of exercise a personneeds to do depends on his or herlifestyle: how active the person is,

how much he or she eats and weighs, body metabolism, and soon. Some people are always on the move and stay relatively fitwithout needing additional exercise. Others sit at a desk all dayand get little exercise. It also depends on what a person wants toachieve. Some people simply want to stay healthy, whereas othersare training for a particular sport, such as marathon running.

Anyone who is starting a strenuous program of exercise needsto build up stamina and flexibility over a period of time. If a longtime has passed since the person did any physical activity, thefirst few sessions will be uncomfortable and the muscles willache. However, the body recovers in a week or two, and thebenefits soon start to show. Sometimes it is unwise to do anyexercise. If people exercise when they are ill—for example, with acold or influenza—it will simply make them feel more exhausted.

Response to exercisePeople respond to exercise in different ways. Most people feel an increase in endurance following frequent and regular aerobicexercise. However, a few people might double their aerobiccapacity, whereas others may not feel much benefit at all. In the same way, only a few people experience significant musclegrowth from sustained weight training; most notice onlymoderate improvements in strength. These differences inresponse to exercise separate the elite athletes from the rest of the larger population.

Too much exerciseIntense physical activity places enormous stress on the body.Carbohydrates, fats, and proteins are used up to release energy.Tiny tears can form in the muscles and connective tissues. The

Exercise

Vigorous sports, such as snowboarding,force the body to take in extra oxygen.That helps improve the function of theheart and respiratory system.


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Training with weights builds up musclesize and strength. That type of exercise,which may involve the use of machines, asshown here, or simple hand weights, keepsthe muscles in a constant state of tension.

stresses are different for different individuals. However, givenenough rest between periods of intense exercise, the body will repair itself and adapt to the training load.

Still, too much exercise is not good for the body. Healthexperts recommend at least one day of rest between intenseexercise sessions to give the body time to recover. In extremecases, overtraining can lead to circulation problems and fatigue.In addition, sudden bouts of intense exercise can damage muscletissue. Repeated damage to tissues caused by overexercising may lead to permanent joint problems later on.

Exercise, eating, and obesityExercise uses up a lot of energy, so it is essential that people eat a healthy, balanced diet. The food must contain the rightbalance of carbohydrates, fats, and proteins, as well as vitaminsand minerals, to replenish the stocks lost during exercise and aid the recovery process.

Obesity is a serious health problem. Many people take in more energy from food than they use. The body converts theextra energy into fat, which is stored in the body. People thenbecome overweight. In extreme cases, that is called obesity,which substantially increases the risk of serious illness.

Children need to take in lots of energy because their body is growing and developing at a fast rate. However, childhoodobesity is becoming more common. It puts children at greaterrisk of diseases usually seen in adults, such as diabetes, blockedarteries, and high blood pressure. Studies have shown thatchildhood obesity is much more common if a child’s parents are obese. There might be a genetic component to obesity, but it is more likely that family members eat the same fatty foodsand avoid physical activity.

Many children get little regular exercise. They spend hourswatching television and playing computer games. Health expertsrecommend that children should do at least one hour of physicalactivity every day. Young people and children should walk orbicycle to school instead of getting a lift in the car—providedthey understand the rules of safety on the highway. A brisk walkis probably the easiest and cheapest form of exercise and can befitted into the daily routine.

Exercise

aerobics • basal metabolism • fats • heart • isometric

exercises • obesity • physical fitness • rest and

relaxation • sports • yoga

SEE ALSO


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Fainting, or syncope, usually starts with a sensation of dizzinessor light-headedness, followed by sudden loss of consciousness.Someone who is about to faint usually turns extremely pale and his or her skin feels clammy. The person may feel nauseated.Breathing becomes quick and shallow, and as the person faints,he or she may fall to the ground. However, most people recoverconsciousness in a minute or so.

The most frequent cause of fainting is that not enough bloodis reaching the brain. Without the oxygen carried by the blood,the brain cannot work properly. People may faint if their bloodpressure is too low to pump enough blood to the brain.

Sometimes, people faint when they stand up suddenly afterlying or sitting down. That is because their blood vessels have not adjusted quickly enough to raise the blood as their positionchanges. Low blood sugar levels (hypoglycemia) can causefainting. Taking sugar or a sweet drink helps resolve the problem.

Severe emotional stress and mild anemia can also causefainting. A psychological shock can make the brain act to slowthe heart and make it beat less strongly, causing fainting.

Heart valve disease may also cause fainting on exertion. In thiscase, drug treatment is required and surgery may be considered.Certain poisons and epilepsy can cause blackouts, or fainting.Immediate medical care is needed in the first instance.

First aid for faintingPeople who faint regularly should talk to their doctor about the problem. Anyone who remains unconscious for more than a minute or two after fainting needs immediate emergencymedical help. If he or she experiences other symptoms, such as numbness or blurred vision, that should also be regarded as a medical emergency.

However, there are a few important rules that can be followed.If someone feels faint, he or she should lie down or sit with thehead lowered between the knees so that blood can flow morequickly to the brain. When someone faints, the person should beturned onto his or her side for at least five minutes, and any tightclothing should be loosened. A handkerchief or sponge should be soaked in cold water, wrung out, and put on the person’sforehead. When the person recovers consciousness, he or sheshould be given a few sips of cold water to drink.

Q & AMy mother is three months’pregnant and has fainted severaltimes recently. Is this harmful?

There is no risk that the baby willbe harmed by these faintingspells (which are not uncommonduring pregnancy), but yourmother may fall over and hurtherself. If she does feel faint, sheshould lie down or sit with herhead between her knees. If thespells become more frequent,your mother should mentionthem to the doctor at her nextprenatal checkup.

SEE ALSOanemia • blood pressure • circulatory system •drinking water • heart • oxygen • skin • tiredness

Fainting

If a person does not recover rapidly from a faint, he or she should be placed in aprone position. This keeps the airway open and lessens the danger of choking.


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The fat in the body comes from fats in the food people eat. Thedigestive system breaks down fats into fatty acids and glycerol.Some fatty acids are broken down at once for immediate energy;if there is any excess, it is stored in the cells under the skin andaround the internal organs.

The rate at which the body burns fat is determined by the rateof energy consumption and controlled by hormones from thethyroid gland, the pituitary gland, and the adrenal glands, whichsecrete adrenaline and noradrenaline. If someone is under stressor getting vigorous exercise, these hormones release more fattyacids into the bloodstream, together with cholesterol. Fatty acidsare converted into the body fuel, glucose, in the liver.

Fats provide more energy, weight for weight, than the othertwo main components of food: carbohydrates and protein. Fatscan also make food taste better. The fats in food are of two kinds,called saturated and unsaturated because of their chemicalcomposition. Most saturated fats, such as butter and shortening,come from animals and are solid at room temperature.Unsaturated fats are liquid and come from fish and plants.

Fats and healthSaturated fats have a bad reputation among dietitians becausethey promote an increase in the tiny transport globules ofcholesterol and protein (low-density lipoproteins) that encouragedeposition of cholesterol in the arteries. Although cholesterol isvital for making cell membranes, bile, and sex hormones and formaintaining the tissues of the brain, the body can make all itneeds in the liver. A high saturated-fat intake interferes with thebody’s own cholesterol-control machinery, and the bloodstreambecomes flooded with cholesterol. Doctors recommend changingfrom eating high-cholesterol, saturated fats to low-cholesterol,unsaturated fats, particularly polyunsaturates. Onions, garlic,olive oil, and oats are among foods that are thought to helplower the levels of harmful cholesterol.

A diet without any fat would be dangerous, as well as boringand difficult to plan. However, it is perfectly possible to surviveon a diet containing only 1 ounce (28 g) of fat a week. A bodyneeds that amount of fat to supply certain fatty acids, which thebody is unable to make for itself. Nearly all fats contain thesefatty acids; fish, soybeans, and canola oil are good sources.

SEE ALSOcalories • carbohydrates • cholesterol • diet • dieting •food and nutrition • health foods • obesity • protein

Fats

A GUIDE TO HIGH-FAT FOODS

Foods containing saturated fatsPercent of fat

Shortening 100Butter 100Coconut oil 100Fried bacon 67Heavy cream 48Cheddar cheese 33.5Broiled steak 32.5Broiled pork sausages 23Ground beef 20Milk 3.6

Foods containing unsaturated fatsPercent of fat

Olive oil 100Margarine (vegetable) 100Peanut butter 48.5Broiled herring 13Broiled mackerel 10Avocado 8

Some foods contain a mixture ofsaturated and unsaturated fats—for example, mayonnaise is 79percent mixed fats, and French fries are 20 percent mixed fats,depending on which cooking oil is used.


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The feet are mechanical masterpieces. Each foot consists ofmany small parts—26 bones, 35 joints, and more than 100ligaments. This structure makes the foot flexible and adapted to walking on uneven surfaces. Most of a foot’s power comesfrom the strong muscles in the leg, helped by a series of smallmuscles in the foot itself.

The weight of the body is supported on the calcaneus, thelargest bone in the foot, which forms the heel, and the heads ofthe five metatarsals, the long bones that link the toes to the restof the foot. The bones are arranged in two arches, which providethe strength needed to hold the body’s weight.

Fallen arches and foot careOne arch runs across the width of the foot. The other arch runsalong the length of the foot and is higher on the inside of the footthan on the outside. If the feet are normal, it is possible to seethe difference in the height of this arch from one side to anotherby making a wet footprint on the bathroom floor. Sometimes, the high side of the arch collapses, because the foot has beenstrained and its muscles are weakened, causing a flat foot.

The feet have to last for a lifetime and provide support, so people should take good care of them. The feet should bewashed at least once a day and dried thoroughly. Socks orpantyhose should be changed every day, and shoes should beaired between wearings. A person’s shoes should have plenty of room for the toes. High-heeled shoes put extra strain on the foot muscles, so they should not be worn all the time.

Chilblains and cornsChilblains are red, swollen areas ofsoft tissue formed where the skinhas been damaged by cold. They mayitch and form ulcers. Chilblains aremost often found on the toes or theoutside of the foot and on the fingerjoints; they can also form on theears, nose, and even the calves.

Chilblains are the result of acombination of cold and damp in an area where the blood flow is reduced. Children often getchilblains because they tend to beout in cold weather and may notwear dry shoes or warm gloves.People with poor circulation are

Q & AMy young sister’s feet turninward. Does this mean she is pigeon-toed?

Yes, it may. Pigeon toes are notusually a big problem, and thecondition often cures itself. It can result either fromdeformities of bones in the foot arch or from weakness in the leg muscles attached to the foot. Your parents shouldtake your sister to the doctor if they are worried.

Feet

The bones of the feet seen from aboveand from both sides.

calcaneus

talus

tibia

metatarsals phalanges


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more likely to get chilblains, as are people who get little or no exercise or whose muscles are wasted by an illness.

Chilblains start as red or purplish blotchy patches that itchand tingle. At this stage, gentle massage and careful warming of the area help. It is important never to scratch these areas.Severe chilblains swell, and tiny blisters containing clear yellow

Feet

COMMON FOOT PROBLEMS

Problem

Athlete’s foot

Bunions

Chilblains

Clubfoot

Corns

Ingrown toenail

Plantar wart

Cause

Fungal infection oftencaught in swimming pools or sports locker rooms, henceits name; aggravated byheavy sweating

Due entirely to wearingshoes that do not fit properly

Contracting blood vesselsdepriving the skin of oxygen;common in people who areextremely sensitive to cold

Generally a congenital defect(present from birth), orcaused by an injury thatinterferes with the foot’snatural growth

Ill-fitting shoes causingpressure points, a buildup of dead tissue, and pain from irritated nerve endings

Shoes that do not fit properly

Infectious wart virus

Symptoms

Splits in the skin betweenthe toes, often spreading to other parts of the foot

Big toe pushed over towardthe other toes, causing adeformity of the jointbetween the big toe and the foot

Swelling, reddening, itching,and a burning sensation;usually affects the fingersand toes when cold

Foot twisted out of its usualposition, with deformedmuscles, tendons, and bones

Painful areas of hard skin on toes, or soft skin between toes

Toenails curving into theflesh; can cause pain,infection, and inflammation

Painful wart on sole of foot,often covered by a callus

Treatment

Keep feet dry, especially afterwashing. Dust with afungicidal powder or rub in a fungicidal cream. Wearclean socks each day,preferably wool or cottonsocks, which absorb sweat.

Correct at an early stage bywearing properly fittingshoes. It is best to consult apodiatrist, who will probablyadvise exercise to correct thedeformity. In extreme cases,surgery may be required.

Prevention is better thancure, so keep the feet warm.Prescribed drugs can improvecirculation.

Some conditions can becured by splinting andmanipulation if treated earlyenough. Special shoes maybe required. Severe cases may require surgery.

Soaking the foot helps, and corn pads may relievethe pressure. A doctor or podiatrist should beconsulted if corns do not respond to simpletreatment.

Shoes should be largeenough. Nails should be kept short. If there is pain or infection, a doctor or podiatrist should beconsulted.

Remove by cauterizing,freezing with dry ice, or surgery.


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fluid may form. In really bad cases, these blisters break down to leave painful ulcer craters. Chilblains usually heal in five to 10 days, but bad cases may take considerably longer. Severe cases need medical treatment. Chilblains can be prevented by wearing warm, loosely fitting clothes in layers and warmlylined waterproof boots or shoes.

Corns, or calluses, are small areas of hard, scaly skin on thetoes. They are the result of repeated rubbing or pressure, oftenfrom tight shoes. Dead skin cells build up, and the deeper skincells underneath become inflamed. Corns feel tender underpressure and may ache at the end of the day. Hard corns occur on the tops of the toes; soft corns develop between them.

Corns are treated by rubbing away the excess skin with apumice stone after a good soaking or by paring off the corn with a special scraper or knife. Corns can also be dissolved with salicylic acid plasters. They are best removed by a doctor or podiatrist.

Feet

Pressure on the top and side of thelittle toe, probably from a tight shoe,has caused corns to form there.

Chilblains are itchy and painful. Ifprecautions are taken in cold weather,chilblains can easily be avoided.

A flat foot (top right) has no inner arch; the complete sole of the foot touches the ground. The inner arch of the normalfoot (bottom right) is higher than theoutside one. The arch of a foot helpsdistribute the body’s weight evenlythrough the heel and toes.

SEE ALSOathlete’s foot • muscle • skeletal system • skin


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Flavonoids are pigments found in plants. They are present infoods such as fruit and soy products and in tea, red wine, anddark chocolate. There are thousands of different flavonoids with yellow, red, or blue, water-soluble pigments, also known as bioflavonoids or polyphenols. Once thought to be simply the waste products of plants, flavonoids are now known to haveimportant physiological functions and protective qualities.

Studies show that flavonoids can kill some disease-formingmicroorganisms, relieve inflammation, strengthen capillary walls,prevent blood clots from forming, and modify the actions ofmany enzymes. Many flavonoids help relieve menstrual andmenopausal problems. Flavonoids give some protection againstcancers and heart disease.

Free radicalsThe damage caused to body tissues by poisons, bacterial toxins, smoking, radiation, many disease processes, and otherdestructive agents arises from the action of chemicals called free radicals. Free radicals attack organic molecules, set up chain reactions in cell membranes and other tissues, and causewidespread molecular damage. To combat these effects, the body synthesizes antioxidants—enzymes that can reverse the effect of harmful free radicals.

Flavonoids as antioxidantsThe principal interest in flavonoids relates to their antioxidantand free radical–scavenging properties. The buildup of cholesterolin artery walls, leading to the development of atherosclerosis, is a major cause of heart attack and stroke. Flavonoids reduce theformation of oxidized low-density lipoproteins (LDLs), which areharmful cholesterol compounds. As a result, flavonoids inhibitthe growth of arterial plaque and help prevent blood clotting.

Flavonoids in wine and chocolateAntioxidant flavonoids are present in red wine, and many doctorsbelieve that this accounts for the fact that heart attacks are rarein French people, who enjoy a high-cholesterol diet and drink a large amount of red wine. Also, people who eat chocolateregularly seem to be less prone to atherosclerosis. That has been attributed to the flavonoid content of chocolate.

Flavonoids

When drunk in moderation, theantioxidant properties of flavonoids in red wine (top) have been found to helpprevent the formation of fatty deposits in arteries. The flavonoids in chocolate(bottom) have a similar protective effect.

antioxidants • cholesterol • heart attack • stroke

SEE ALSO


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The label on any food can, bottle, or package must list all theingredients. Some of these may be familiar. Others may havestrange-sounding chemical names, and some are just vaguedescriptions such as artificial coloring. However, all of theseingredients have to be approved by the Food and DrugAdministration (FDA).

There are several kinds of food additives, including colorings,preservatives, flavorings, texturizers, thickeners, emulsifiers, and supplementary vitamins and minerals, which are added to increase a food’s nutritional value.

One reason for clear labeling of foods is that a few people areallergic to some additives. Many of the additives, however, comefrom natural sources, and many more are closely relatedchemically to the food products they are found in.

PreservativesWithout preservatives, the vast variety of food on supermarketshelves would not be available all year round. Preservatives areused to stop food from being spoiled by the growth of bacteriaand fungi. They also stop food from deteriorating naturally, andthey stop oxidation, the process that turns cut apples brown.

Traditional preserving methods such as salting and pickling in vinegar do much the same job as modern preservatives. Theyare no more natural, however, than modern methods. Salt andvinegar are both chemicals—sodium chloride and acetic acid,respectively. Modern additives such as butylated hydroxyanisole,propionic acid, and sulfur dioxide are closely related to chemicalsthat are commonly present in food. Vitamin E and vitamin C arehealth-giving substances that are also used as preservatives.

Q & AI’m allergic to monosodiumglutamate. Does this mean I can’t eat Chinese food?

The food prepared at Chineserestaurants may contain a lot ofmonosodium glutamate (MSG),and it is an important ingredientin soy sauce. Few people areallergic to MSG, and the smallamounts added to many foodsseem to have little or no effect.People who are allergic to it cansimply ask for MSG to be left out of their meals at Chineserestaurants.

Is it true that if all coloringswere removed from foods, thefoods would not look appealing?

Food color is added to enhanceappearance. For example,processed peas would lookunappetizing without addedcolor. Simulated colors can makethe real thing look pale incomparison. Food color can alsosuggest a high nutritional value;yellow coloring in cakes suggeststhat they are rich in eggs.

Food Additives

This is a selection of bright food colorings that are routinely added to many foods,including juices and drinks, baked goods,and frozen foods.


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Coloring and flavoringMany foods lose their natural color when they are processed.They look pale and unappetizing. To make food look moreappealing, manufacturers add coloring. Some colorings arenatural substances, such as chlorophyll.

Flavoring is also added to make food more palatable. Mostflavorings are natural extracts that are easily recognized. Thesubstance monosodium glutamate (MSG), which has hardly anyflavor itself, has the remarkable property of making meat andfish more flavorful. MSG is often added to Chinese food, althoughsome people react badly to large amounts of this additive,experiencing such symptoms as headaches and chest pains.

Other substancesTexturizers change the consistency of food. Many familiar foods,such as commercial ice cream, would be very difficult to producewithout them. Commercial ice cream contains glycerolmonostearate (GMS), which makes it creamy, plus gums andalginates (seaweed extracts). Other common texturizers includegelatin (which makes cheesecake smooth) and pectin (whichmakes jellies set). Added vitamins and minerals rarely increase the nutritional value of foods, except when they are added toreplace vitamins and minerals that are lost in food processing,as in milling flour or canning.

Food Additives

SEE ALSOappetite • diet • food and nutrition • food labeling •food poisoning • minerals • vitamins

COMMON FOOD ADDITIVES

The following are some of themost common food additives that are listed on cans, jars, and cartons:

Preservatives• Acetic acid (vinegar)• Butylated hydroxyanisole (BHA)• Butylated hydroxytoluene (BTA)• Citric acid• Sodium benzoate• Sodium chloride (salt)• Vitamin C (ascorbic acid)• Vitamin E

Thickeners, emulsifiers, and texturizers• Glycerol monostearate (GMS)• Lecithin• Pectin• Vegetable gums• Agar• Carrageen• Soy• Gelatin• Guar gum

Sweeteners• Saccharin• Sucrose (sugar)

Flavoring• Monosodium glutamate (MSG)

Additives are even added to sugar topreserve it and make it taste morepalatable to the consumer. Here, theinput of additives at a sugar refinery in Florida is being adjusted.


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Foods contain the nutrients that are essential for life. Withoutfood, all living organisms—plants and animals, includinghumans—eventually die. To grow strong and healthy, peopleneed regular, well-balanced, nutritious meals, and snacks shouldbe healthy ones. Food provides both the materials from whichhumans make their body tissues and the energy they need tokeep alive and active.

Plant and animal foodPlants get their nutrients and water from the soil and the air.They grow with the help of energy from sunlight. Animals useplants and other animals as food. They also need water to drink.The process by which plants and animals take in and make use of their food is known as nutrition. In the last 100 years or so,scientists have discovered a great deal about nutrition. Theyknow which foods people (and plants and animals, too) need to grow strong and to keep healthy. They have found that somediseases are caused by the lack of certain substances in the diet.They have also found that too much of certain foods can causeboth short-term and chronic illnesses.

Food choices Many people do not have much choice about what they eat or even have the option of eating every day. They may live incountries where food supplies are limited or they may not have

Q & AI want to become a vegetarian,but my parents are concernedabout whether or not I’ll be able to get all the vitamins andother things that I need. Can’tmy nutritional requirements beproperly met without eatinganimal proteins?

Animal proteins are convenientsources of essential amino acidsin a normal diet. However, avegetarian diet composed of amixture of proteins from cereals,grains, nuts, and dairy productswill give you a proper balance ofall the nutritional elements andvitamins, if you consume enoughof these foods.

Do illnesses have any effect on our nutritional needs?

Yes. Many illnesses, especiallyinfections, increase the body’sdemands for calories, proteins,and certain nutrients. However,the appetite is usually reduced at the same time. That accountsfor the weight loss that oftenaccompanies some chronicinfections. Some tumors mayincrease the need for certainnutrients by stepping up theturnover of specific chemicals in the body.

Food andNutrition

Oranges are an importantsource of dietary fiber and vitamin C.


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much money to spend on food. Sometimes, theysuffer from nutritional diseases. In other countries,such as the United States, there is an immensevariety of food available, and people are more likelyto suffer diseases of overeating, such as obesity and heart problems. However, more and morepeople are now interested in eating healthily. If people know about the nutrients the body needs and the foods in which those nutrients are found, they can eat healthily without spendingtoo much money.

Limiting cholesterolIdeas about the best possible diet are continuallychanging. For example, there have been manyrecommendations during the last few years abouthow many eggs a person can safely eat each week.Opinions vary, but the American Heart Associationstill recommends no more than four eggs a week.

The association also suggests limiting totalcholesterol consumption to 300 milligrams a day.

In other words, people should cut down on foods with a highsaturated fat content, such as meat, poultry, and dairy products.In addition, it is recommended that everyone should exercise andmaintain a healthy body weight.

It is also best to avoid saturated fats present in crackers,cookies, pastries, cakes, doughnuts, french fries, potato chips, andpuddings, because these foods are known to increase the badLDL (low-density lipoprotein) cholesterol in the blood. LDLcholesterol is the type of fat that is deposited in the arteriesaround the body and causes disease. The good HDL (high-densitylipoprotein) picks up loose molecules of cholesterol and returnsthem to the liver, where they are broken down; they are theneliminated from the body.

Essential nutrients The nutrients that are essential for life are protein, minerals, fats, carbohydrates, and vitamins. In addition, people need plenty of water. Together, these nutrients will give people

Food and Nutrition

Eggs for breakfast? Until recently, people thought it washealthy to eat an egg a day. Now, some nutritionists believethat people should not eat more than four eggs a week,because eggs contain a substance called cholesterol, whichplays a part in diseases of the arteries and heart.


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the materials for making and repairing body tissues and the energy for carrying out everyday activities.

The energy people get from food is measured in units calledcalories. If people eat food containing more calories than theirbody uses, the extra calories are stored in the body as fat. Ifpeople eat fewer calories, the body draws on its fat stores forenergy and weight is lost. Growing children and people whoexercise a lot or do hard physical work use up more calories thanpeople who are inactive. Children and active people need to eatmore calories. To stay at the same weight, people need to eatonly as many calories as they use.

Food and Nutrition

ESSENTIAL NUTRIENTS

Proteins provide the chemicalcompounds from which all the cells of the body are made. People needproteins to make new tissues andrepair old ones. Proteins are also usedto make the antibodies that fightinfections. They help people digestfood and supply them with energy.Proteins are present in animalproducts, including meat, fish, eggs,and milk, and in some vegetableproducts, including nuts, peas, beans,and legumes. The body cannot storeprotein, so it is best to eat some foodscontaining protein every day.

Fiber is present in vegetable foods. It is made of materials such as celluloseand pectin. Humans cannot digestfiber. It provides no nutrients, but itplays an important part in a healthydiet. Fiber helps move food efficientlythrough the digestive system. Its bulk stimulates peristalsis, the wavemovement that pushes food along the digestive tract. Fiber may also have a helpful effect on the way inwhich the body uses fats. Studies have shown that people in developingcountries whose diet is high in fiberare less likely to develop diseases suchas cancer of the colon. Also, peoplewho eat plenty of fiber rarely sufferfrom constipation. Nutritionists nowsuggest that everybody should eat a diet high in fiber. Fruits, leafyvegetables, legumes, and unrefined

cereals are all high in fiber. Processingremoves fiber as well as nutrients.

Carbohydrates, which are present instarchy and sugary foods, are majorsources of energy and supply most of a person’s calories. Cereals, bread,potatoes, rice, and pasta are high in complex carbohydrates. Simplecarbohydrates (sugars) are present incookies, cakes, and candies. Sugar ishigh in energy but provides “empty”calories with no vitamins or minerals.Sugar also encourages tooth decay.Extra calories present in starch andsugar are stored as fat.

Fats provide energy and some essentialvitamins and acids. They also makefood taste pleasant. Fats are present in milk, meat, olives, nuts, and seeds.Excess dietary fat is stored in the bodyas fatty tissue. Animal fats, and fatsfrom some plants, are saturated fats.Eating too much saturated fat can raise the blood cholesterol level.Unsaturated fat, which is present in fish, chicken, turkey, and mostvegetables, is healthier to eat.

Vitamins are chemicals that the bodyneeds to function properly. Vitamin Ahelps people see well in the dark, andvitamin C keeps the blood vesselshealthy. Vitamins C and E are anti-oxidants. Vitamin K helps the blood clot.Vitamins are present in fruits, vegetables,

milk, and meat. Methods used for foodprocessing and long storage of food canmake supplementation with vitaminsnecessary. Extra vitamins should betaken only if a doctor recommends them.

Minerals are essential for good healthand to keep the body working properly.Iron is needed to carry oxygen aroundthe body in the bloodstream; calciumand phosphorus build strong bones.Each person needs only small amounts,and people eating a sensible daily diet should get enough minerals in their food. Pregnant women mayneed extra iron but should takemineral supplements only if a doctoradvises this. Salt is a mineral; too much salt can be bad, particularly if someone has hypertension (highblood pressure).

Water is essential; it makes up morethan half of the body content. It helpsin the digestion and absorption offood, carries food to the tissues, andcarries away waste products. Peoplecan live for weeks without food butwould die in a few days without water.The body loses 4 pints (1.9 l) of waterdaily in urine, feces, perspiration, and the moist air that is breathed out.About 70 percent of food consists ofwater, but people should also ensurethat they drink at least eight cups (1.9 l) of liquid a day, preferably in theform of water rather than other drinks.


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Food groupsTo help people know what they should be eating, scientists havedevised a food pyramid that divides foods into different groups,which are represented by six differently colored bands. Thedifferent sizes of the bands show the proportion from each food group that should be eaten each day. The wider the band at the base, the more of that food should be eaten. Thenarrowest band (yellow) represents oils and fats, which should be eaten sparingly. The bands that are widest at the base remindpeople to eat mostly foods without solid fats and added sugar.The emphasis is on a high-fiber, low-fat diet. Whole grains, fruits, and vegetables are extremely important food items.

This system was designed to help people make healthier foodchoices. It also reflects the government’s new dietary guidelines,including the importance of balancing what people eat withtheir physical activity; the steps at the side of the pyramidremind people to be active every day.

The orange band represents grains. Everyone should aim to eat 3 ounces (84 g) of whole-grain bread, cereals, rice, or pastaevery day. Vegetables are represented by the green band. Peopleshould vary their choices and include dark green, leafy, andorange varieties, plus dry beans and peas. Spinach, carrots, andsquash provide vitamin A, and many vegetables also providevitamin C, calcium, iron, and fiber.

The red band indicates fruits, which can be fresh, frozen,canned, or dried. Citrus fruits, tomatoes, strawberries, pineapples,canteloupe, and papaya are rich in vitamin C and also contain

Food and Nutrition

For many years, scientists have been usingthe concept of a food pyramid to helppeople understand about healthy eating.The pyramid shown here was newlydesigned in 2005 by the United StatesDepartment of Agriculture to emphasizethe importance of both diet and exercise.

STEPS TO A HEALTHIER YOU

grains

oils milk products meat and beans

vegetables fruits


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vitamin A, iron, and calcium. Othervegetables and fruits containvitamins B1 and B2, calcium, iron,minerals, carbohydrates, and fiber.

Small amounts of oils or fats(yellow band) should be chosen fromfish, nuts, and vegetable oils. Solidfats such as butter, lard, andshortening should be avoided ifpossible. Milk products (blue band),including cheese, milk, and yogurts,should preferably be fat-free or low-fat—the protein and calciumcontent is the same, but the fat has been removed.

Meat and beans are protein-richfoods that are represented by thepurple band. It is best to choose low-fat or lean meat and poultry and tovary the choices to include more fish,beans, peas, nuts, and seeds.

Harmful fats occur in many foods.Often, they are hidden in cakes andcookies, along with added sugarsthat do nothing but make peopleoverweight and unhealthy. Everyoneshould eat as few of these types offoods as possible. It is also better to avoid foods fried in oils or fats, as well as sweets and candies madewith butter, sugar, and cream.

Preparing and choosing carefullyThe best food ingredients can do little good if they are notproperly prepared. An example of this is the way in which rice ispolished to remove its husks. Some people think that polishedrice tastes better, but removing the husks also removes most ofthe nutrients. Many people suffer from deficiency diseases thatcould have been prevented by eating unpolished rice. In a similarway, white flour and its products are often used instead of wholewheat, even though much of the goodness has been removed. Inthe United States, nutrients are added to white flour to replacethose lost in the milling. Nutrients are also added to foods suchas milk and margarine to help ensure that people get enoughvitamins and minerals.

Food and Nutrition

Dairy products (top) such as cream,butter, and cheese are all high insaturated fats. So are bacon, sausages,and red meat. Avocados also contain fat,but it is the healthier, unsaturated type.Whole-wheat bread and fresh fruits(bottom) contain dietary fiber, animportant substance that helps keep the body functioning efficiently.


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Cooking food by an appropriate method is an important factorin how beneficial it is. For example, frying depletes nutrients, and vitamins A, B, C, D, E, and K are lost. Vegetables cooked for too long in large amounts of water lose vitamins and minerals.

It is also important that food is grown and prepared inhygienic conditions; otherwise, it may be contaminated withharmful chemicals or disease-causing organisms. Food shouldalways be fresh; fresh or frozen vegetables contain more vitaminsthan wilted ones.

Changing habitsMaking food look and taste good makes it more appetizing andeasier to eat. Taste is partly a matter of habit; people like thetastes they are used to. However, tastes can be changed, andbecause it is now known that eating too much saturated fat,sugar, and salt may be harmful, more cooks are using only smallamounts of these substances in their food.

Different foods may taste strange at first, but people soonlearn to enjoy the new flavors. Many people now substitute thehealthier polyunsaturated fats, such as corn and sunflower oils(and spreads made from them), for butter and shortening.

There are sometimes hidden dangers in food. For example,many processed foods include sugar and salt, and chocolate and

Food and Nutrition

Food should look good as well as tastegood, to encourage people to eat. Thismeal contains a good balance ofingredients. It looks appetizing as well as being healthy.


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candy contain large amounts of fat. Soft drinks are often high insugar; diet, low-sugar, or reduced-calorie versions are healthier.Food additives, which are substances added to foods to improvetheir color or flavor, or to preserve them longer, can cause allergicreactions in some people.

As people have become much more conscious of the harmthey can do to themselves by not eating sensibly, many havestarted to change their food habits. Before long, healthy eatingmay become the norm and people will lead a longer andhealthier life.

Food and Nutrition

SEE ALSOanorexia and bulimia • calories • carbohydrates •cholesterol • diet • dieting • fats • food additives •food labeling • minerals • nutritional diseases •obesity • protein • sugars • vitamins • weight control

Some foods, such as cheeseburgers andchocolate sundaes, are popular withmany people, but this type of junk foodcontains high levels of sugar and harmfulfats. Mixed salad and fresh fruit, properlyprepared and presented, are attractiveand make far healthier alternatives. Oncepeople get used to eating fresh foods suchas these, they may find the taste of junkfood less appealing.


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The aim of food labels is to provide people with usefulinformation about the food they eat and to help them makebetter choices. Food labeling follows legal rules set out in 1990 by the Nutrition Labeling and Education Act. These rules weredesigned by the U.S. Food and Drug Administration (FDA).

By law, all food labels must contain the common name of thefood, the name and address of the company that made it, andthe amount present (usually by weight). Freshness dates aremarked, and labels must list the ingredients in order of content.

The law also requires food labels to provide nutritional data.All the facts are based on one serving, so the first thing the labelmust identify is the size of one serving. Nutritional facts includethe proportions of carbohydrates, fats, and proteins present inthe food, as well as any vitamins and minerals. The label mustshow the energy value of the food, measured in units calledcalories, as well as how much energy comes from the fat contentof the food. Finally, the label must show the recommended dailyallowance (RDA) for each nutrient. The RDA is measured as apercentage of an average dietary intake of 2,000 calories eachday for women and 2,500 calories each day for men.

Health claims and food additivesThe FDA sets standards for the claims food manufacturers use to promote their products. Onecommon example is the term lowfat. According to the FDA, a foodcan be labeled as low fat when itcontains 3 g or less per serving.Similar definitions exist for manyother terms used on food labels.

Substances called food additivesimprove foods in various ways.Preservatives help food stay fresherfor longer, and salt, spices, andsweeteners make food taste better.Dyes improve color; vitamins andminerals add nutritional value.Some additives may cause healthproblems in people with allergies,so the label must list all additives.

Q & AI’m confused about thedifference between calories andkilocalories. And where doesenergy come in?

A calorie is defined in terms ofenergy as heat. A calorie is theamount of heat required to raise1 g (1 cc) of water by 1°C. That istoo tiny for nutritional purposes,so all food labeling uses a unit that is 1,000 calories or 1 kilocalorie. Therefore, anutritional kilocalorie is theamount of heat required to raise 1 kg of water by 1°C.

Will a food label tell me if thereis coloring added to a product,and do I need to worry about the effects?

A label will tell you if a coloringhas been used, but if it statesthat the product has no artificialcoloring, read the otheringredients carefully. If you areworried about the effects ofcoloring, get a book that lists theeffects of specific colorings froma health food store.

SEE ALSOcalories • diet • dieting • fats • food additives • food

and nutrition • health foods • weight control

Food Labeling

Everything in this can must be listed on the label, together with information such as amount, nutritional data, energy values, and freshness.


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Food poisoning results from eating food contaminated withbacteria or chemicals, or some other poisonous substance.Although the causes vary, the main symptoms are the same:vomiting, pain in the abdomen, and diarrhea, which all beginwithin a few hours of eating. Most people recover quickly, but the symptoms can be dangerous for children and elderly people.If symptoms are severe, a doctor should be called.

Food is easily contaminated with bacteria unless it is storedand handled hygienically. It is important to wash the handscarefully before touching food or eating and to keep kitchens and utensils clean. People should never prepare food if they haveboils or other infections on their hands. Similarly, people shouldnever accept food from a food handler with infected hands.

Infective bacteria in food include salmonella, dysentery, and paratyphoid bacteria. They can come from uncooked orundercooked food or from food that has been cooked when only partially defrosted. Poisons (toxins) can also be produced by bacteria in food, including staphylococcal bacteria andClostridium botulinum. Botulism is a rare but dangerous form of food poisoning that results from eating contaminated, badlypreserved food. Anyone with botulism needs immediate hospitaltreatment, because the infection is life-threatening.

Shellfish living in polluted water are often contaminated, sopeople should be careful where they get shellfish from. Fruitsand vegetables should be washed to rid them of insecticides that have been sprayed on them. Mushrooms or berries shouldnever be eaten unless one is sure that they are not poisonous.

Q & AMy grandmother says that a bitof dirt won’t do you any harm. Is she right?

Generally, yes. Household dirtcontains millions of micro-organisms; if eaten, most ofthem are destroyed by the acidin the stomach before they cancause illness. This is why childrencan eat sand or even worms and come to no harm. Dirt lefton food, however, can breedbacteria, which produce toxinsthat cannot be neutralized bystomach acid. Bacterial toxinscan cause food poisoning, suchas salmonella and dysentery.

Food Poisoning

Undercooked meat should never beeaten. Uncooked and cooked meatsshould never be stored together.

No one should risk even tasting agrowing mushroom. Deadly ones can look identical to harmless ones.

Polluted water can contaminateshellfish. A cooked but unopenedmussel must never be eaten.

digestive system diseases and disorders • salmonella

SEE ALSO


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A fracture is a break in one of the bones of the body. Somefractures are simple breaks that heal quickly and easily; in other,

more serious fractures, the bonesmay be broken into several pieces.This type of break requires skilledtreatment and takes time to healproperly. A dislocation is thedisplacement of a bone from itssocket or from an associated bone.

A simple (closed) fracture is one in which a bone is broken but theskin is intact and the tissues aroundthe break are virtually unharmed. In a compound (open) fracture, theskin is broken by the bone. This typeis more serious because there is amuch greater risk of infection. Whenthe bone has broken into severalpieces, the fracture is described ascomminuted. When one end of thebroken bone has been driven intoanother bone, it is an impactedfracture. A depressed fracture is onein which the broken bone is pressingdown on the structure underneath.Sometimes, the bone is not brokenright through but is simply cracked.Such fractures are known asgreenstick fractures. That type ofinjury is most common in children,whose bones are still growing andare relatively supple.

It takes a great deal of force tobreak a healthy bone. Fractures aremost often caused by accidents such as falls. Elderly people, whosebalance is poor, fall more often, and their bones tend to break more easily than those of youngerpeople. Some diseases, includingosteoporosis, make the bones sobrittle that they break for little or no apparent reason. These types of fractures are known aspathological fractures.

Q & AMy parents and I are planningour first skiing vacation. I don’twant a broken leg. What can I do to minimize the risk?

You can make sure that you arephysically fit before you go. Starttoning up your muscles for a fewweeks before you leave. Jogging,in-line skating, and bicycleexercises are very good for theleg muscles. Better still, take a skiclass, which will certainly saveyou from a few unnecessary falls.

A few months ago, my motherslipped on ice and dislocated hershoulder. She had it put back inplace but has had a lot of achesand stiffness since then. Is thereanything she can do about it?

Pain and stiffness after adislocation are common.Physiotherapy will improve jointmobility and aspirin may helprelieve the pain. Occasionally, aninjection of a steroid drug intosurrounding tissues is required.

Fractures andDislocations

In this comminuted fracture of the femur(thighbone), the bone has shattered intosmall pieces. Treatment involves operatingto remove fragments, joining the bone ends with a metal plate, andimmobilizing the limb in plaster.

comminutedfracture


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Fractures and Dislocations

The supple bones of babies and childrenmay bend and crack rather than breakcompletely. This sort of injury is known as a greenstick fracture (top). The limbshould be immobilized in a plaster cast. In a compound fracture (bottom), thebroken bone pierces the skin. Damagedtissue and bone fragments must beremoved, the bone must be realigned, and the limb must be set in plaster.

FIRST AID FOR FRACTURES

Do• Call for an ambulance• Make patients comfortable

(moving them as little as possible)

Do not• Give the patient anything to eat

or drink, or a painkiller, in case an anesthetic has to be given when the bone is set

• Try to realign the fracture yourself; you could cause damage

greenstick fracture

compound fracture

Symptoms and treatmentThe most obvious symptom of a broken bone is pain, anddamaged tissues in the area around the break may cause thearea to swell and look deformed. Movement and pressure maymake the pain worse. Broken bones in the hands and feet andbroken ribs may be mistaken for sprains or torn muscles, but a limb that is broken cannot be used. The chief danger from afracture is shock, caused by pain and blood loss. Bone, like anyother tissue of the body, has a rich blood supply; the bigger thebone that breaks, the greater the loss of blood. Broken bones may also damage the tissues around them.

Broken bones need medical treatment. A doctor should be called, or the person should be taken to the hospital byambulance. The victim should be moved as little as possible,particularly if there is any danger of a back injury. When thepatient reaches the hospital, he or she will be treated for painand shock and given an X-ray to assess the damage. The brokenbones will then be put in the correct position. A shattered orawkwardly broken bone may need to be repaired with a metalplate screwed along the bone. Some breaks, such as rib fractures,can be left to heal by themselves, but most fractured bones needto be held in position as they heal. This is often done by encasingthe area in a plaster cast; a leg may have to be in a cast for 12weeks or more before it is strong enough to take the body’sweight. Bones usually heal extremely well, and in many cases, the fracture leaves no outward sign once it has healed. It mayeven be difficult to see on a later X-ray.


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Fractures and Dislocations

The shoulder normally has a rounded contour. If thehumerus (armbone) slips outof the scapula (shoulderblade) socket and becomesdislocated, it makes theshoulder take on a square shape (inset).

DislocationAnother type of bone injury is adislocation, in which the bone of a joint is wrenched out of its socket.A dislocated bone is extremelypainful because the force of theinjury damages the tissues, nerves,and blood vessels around it. The joint swells and needs treatment as quickly as possible. A skilledtherapist may be able to put thebone back in position if it is treatedimmediately, but after 15 minutes or so, the swelling is so great that ageneral anesthetic is necessary. Theshoulders, thumbs, and fingers arethe joints most often affected; othersinclude the jaws, elbows, knees, andhips. Some babies are born withdislocation of the hip, which isusually cured by putting the hip in a stabilizing sling for a few months.

This person has suffered a broken wristand has had the injury set in a plastercast that holds together the broken bones to allow them to heal properly.

SEE ALSOpain • skeletal system • sports injuries • sprains and

strains

humerus

scapula


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Glands are organs that manufacture and secrete substances to perform various functions in the body. There are three maingroups of glands: endocrine glands, exocrine glands, and theglands of the lymphatic system. The major endocrine glands—the pituitary, adrenals, thyroid and parathyroid, pancreas, ovaries,and testes—secrete hormones directly into the bloodstream,where they are taken to their target tissues, which are thenstimulated into activity. Exocrine glands, such as sweat glands,release a secretion externally, via a canal or duct, to the body’ssurface. Finally, the lymphatic system produces antibodies and special blood cells called lymphocytes.

The endocrine glandsThe body is like a finely tuned musical instrument, with theglands of the endocrine system keeping all the parts working in harmony.

The endocrine system controls many of the vital functions ofthe body. In turn, the endocrine glands are controlled by a part of the brain called the hypothalamus, which is attached to a master gland called the pituitary, situated at the base of the brain. The pituitary is fed stimulating hormones by thehypothalamus; these hormones act on the other glands in a feedback system. For example, the thyroid gland producesthyroid hormone, which is essential to keep all the body systemsactive. If the level of thyroid hormone is too low, the pituitaryreleases thyroid-stimulating hormone to urge the thyroid toproduce more of its hormone. Once the level rises, the feedbackmechanism ensures that no more stimulating hormone isproduced until it is needed. The parathyroid glands are alsostimulated by the pituitary to control calcium and phosphoruslevels in the blood.

The pituitary gland also controls the release of hormones from organs to ensure that bodily functions are carried out. Forexample, the pituitary gland stimulates the adrenals to releasecorticosteroid hormone, which affects metabolism; adrenalineand noradrenaline to increase heart rate and blood flow tomuscles; aldosterone to regulate salt excretion; and cortisol to boost sugar levels. The ovaries and testes are stimulated to release male and female sex hormones; and the pancreas,both an endocrine and an exocrine gland, is stimulated toproduce two hormones: insulin to regulate blood sugar levelsand glucagon to increase blood sugar levels. Apart from itsstimulatory function, the pituitary secretes growth hormone;prolactin, to help produce breast milk; a hormone to regulatewater balance; and one to contract the uterus (womb) in labor.

Q & AIf glands stop working, is itpossible to perform a transplant?

No, but other treatment can begiven. If the endocrine glands(which form the hormonesystem) stop working, ahormone substitute can be givenby mouth. If the pancreas stopsproducing insulin, diabetesresults. That is treated withinsulin by injection.

I had infectious mononucleosis,and my friend said it was aglandular disease. Was she right?

A common feature of infectiousmononucleosis is a swelling ofthe lymph nodes, and peopleoften refer to this as a swellingof the “glands.” However,infectious mononucleosis is a disease that affects the wholebody, rather than the lymphnodes alone.

My armpits smell. Is it possibleto remove the sweat glands?

Sweat does not smell offensiveuntil it begins to decompose. Thesolution is frequent washing andusing a deodorant. Also, consultyour doctor; he or she canrecommend other treatments.

Glands


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The exocrine glandsThe exocrine glands release secretions tothe surface of the body. For example, sweatglands produce sweat, secreted throughpores in the skin. Modified sweat glands inthe ears produce earwax. Sebaceous glandsin the skin produce sebum, which keeps theskin supple. Tear glands produce fluid tolubricate the eyes, and mammary glandsproduce milk. Other exocrine glandsproduce digestive fluids. These glandsinclude the salivary glands, the pancreas,glands in the lining of the stomach and theintestines, and the liver.

The lymph nodesThe lymph nodes, which are commonly, but incorrectly, referredto as glands, are part of the lymphatic system. This system is anetwork of lymph vessels and lymph nodes. The lymph nodescontain lymphocytes, which are blood cells called white cells that help fight the spread of infection. Lymph nodes vary in sizefrom microscopic to 1 inch (2.5 cm) in diameter.

The pineal glandDeep within the brain, the pineal gland secretes the hormonemelatonin, which affects the regulation of the day-night internalbody clock. This hormone is secreted mainly during the hours ofdarkness and is not produced when bright light enters the eyes.If given as a drug, melatonin alters the body clock settings, so it is sometimes taken to prevent jet lag.

Glands

This diagram shows the location of the endocrine and exocrine glands in awoman. The yellow spots indicate lymphnodes, which are known as glands but are part of the immune system, alongwith the thymus. The pineal glandcontrols body rhythms such as wakingand sleeping. A man’s glands are thesame, except for the reproductive glands(above right). Whereas a woman hasmammary glands and ovaries, a man has testicles (which producetestosterone), seminal vesicles,bulbourethral glands, and a prostategland (which produces seminal fluid).

thymus

ovary

salivary glands

thyroid gland

mammary gland

pineal gland

seminal vesicles

prostate

bulbourethral glands

testicles

pituitary gland

parathyroidglands

stomach

pancreassmallintestine

sweatglands

adrenal gland

FEMALE GLANDS MALE GLANDS

SEE ALSObody systems • calcium • digestive system • growth •salt • skin • sugars • sweat


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From the time an egg is fertilized to the birth of a baby takes justnine months. This is the most rapid stage of all in the body’sgrowth and development, but a newborn baby is still tiny andhelpless. It takes approximately 9 to 10 years before a child isphysically capable of being independent, and even longer beforemental development is complete.

InfancyAt first, a newborn baby can do little more than suck, swallow,and grasp. During the first year of life, however, the body growsextremely quickly. Nerves develop their interconnections, and asthey develop, babies are able to learn to control their movementsand to make sense of their surroundings.

After the first year, physical growth slows down and thetoddler enters a steadier period of growth, during which moreintricate skills are mastered. Each stage in learning, includingwalking, talking, and reading, depends on the development of the brain and nervous system.

When a baby’s bones are first formed, they are made of aflexible tissue called cartilage. As the limbs grow, the cartilage is replaced by fibrous tissue, which gradually solidifies into hardbone, a process known as ossification. At birth, much of theskeleton is still cartilage, and the bones of the skull have not yetjoined together; instead, they are flexible, to allow the baby topass quite easily through the mother’s narrow birth canal.

ChildhoodAll through childhood, and until the body is fully grown, new

cartilage cells are made to increase the size of thebones. The bones becomelonger, thicker, and harder,until they stop growingcompletely by the mid-20s.At the same time, all theother cells in the body areincreasing in number andgrowing larger.

From about age threeuntil adolescence, childrengrow approximately 2 to 3 inches (5–7.5 cm) a year. As children grow, theproportions of their bodieschange as parts develop

Q & ADo all children have a growthspurt?

Yes. The rate of growth tends to be fairly steady until theadolescent growth spurt, whichoccurs at around the age of 11 ingirls and later in boys, althoughthe timing and extent arevariable. The average 13-year-oldgirl tends to be slightly tallerthan a boy of the same age; he will catch up later.

My 15-year-old cousin seems to be growing and growing.When will he stop?

The average age for upwardgrowth to stop is around 17 forboys and 15 for girls, but there isoften a variation of at least twoyears on either side. In yourcousin’s case, it all depends onthe time when his growth spurtstarted. On average, the rate ofgrowth will fall to around 1 inch(2.5 cm) a year within three yearsafter the growth spurt starts.

Growth

A nine-week-old fetus is just 0.9 inch (2.3 cm) long. All the body parts arepresent, although they are not fullyformed. By the end of pregnancy, the 40-week-old fetus will have fully grown to about 20 inches (51 cm) in length.


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at different rates. For example, a baby’s head is much larger inproportion to its body than an adult’s; its head, therefore, willgrow less than the rest of its body.

AdolescenceThroughout childhood, girls are on average around 0.5 inch (1.3 cm) shorter than boys. At about 11, however, girls undergo a sudden increase in height, known as the adolescent growthspurt. They may grow taller than boys of the same age, who start this spurt about two years later. Everything grows duringthis time—bones, muscles, and organs such as the heart.

Many children change in appearance as the shape of their face changes. The forehead, nose, and chin become less roundedas fat disappears from the face. Boys broaden at the shouldersand girls widen at the hips. The secondary sexual characteristicsdevelop in both girls and boys. Often, this growth is uneven, withmuscles growing more slowly than bones, so that adolescentslook gangling and out of proportion. In the late teens, growthslows down, and by the early 20s, the body is fully developed.

Variations in growthGrowth is controlled by various hormones produced by the body,including growth hormone, thyroid hormone, and sex hormones.If too much or too little of these hormones is produced, growth

will be affected. Children’s growth should bechecked regularly by a doctor. If they are notdeveloping normally, it may be possible totreat them with the appropriate hormone.Some diseases, and a diet that lacks certainnutrients, may also hinder growth.

Many parents and children worry about the rate of growth during childhood. It isimportant to remember that this rate variesconsiderably. Two normal, healthy childrenwho are age seven may differ by as much as 8 inches (20 cm) in height. Girls may begintheir growth spurt anytime between 9.5 and 14.5 years; boys may begin their growth spurtbetween 10.5 and 16 years.

Understandably, those children who startgrowing late may worry that something iswrong, but there is usually no problem. It issensible to see a doctor, however, because in most cases he or she will be able to givethe necessary reassurance.

Growth

These teenage girls have had theirgrowth spurt. Between the ages of 9.5and 14.5 years, girls suddenly becomemuch taller, the shape of the facechanges, and they develop secondarysexual characteristics, such as breasts and broad hips.


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HormonesA person’s rate of growth is controlled by various hormones, two of which are particularly important: growth hormone andthyroxine. Growth hormone is produced by the pituitary glandand thyroxine by the thyroid gland, which lies at the base of the neck. If someone’s body is not producing enough of thesehormones, growth will be slowed down, although the bodyremains in proportion. Giving the person additional hormonesmay allow him or her to develop normally.

GigantismIf a child grows much taller than normal, he or she may besuffering from a condition known as gigantism. This disorder is caused by an overproduction of growth hormone by thepituitary gland, a pea-size endocrine gland situated in the brain.

Although it is usually possible to stop the extra growth, peoplewith the disorder have been known to reach 8 to 9 feet (2.4–2.7m) in height. They are generally in proportion, although theyusually have extremely large hands and feet.

In some cases, the excess of growth hormone begins after thelong bones of the body have stopped growing, in the mid-teens.Then, the hormone causes a disorder known as acromegaly. Thebones of the face, jaws, hands, and feet slowly thicken, and thesoft tissues of the face, ears, and nose grow thicker, too.

Excess growth hormone is usually caused by a tumor in the pituitary gland. The tumor can be removed by surgery ordestroyed by radiation. If the pituitary gland is destroyed by the tumor, the patient will be given replacement hormones.

DwarfismPeople who are unusually short in height, although generallynormal in other ways, have traditionally been called dwarfs. Since the term may be hurtful to a person of short stature,thoughtful people now avoid this terminology.

A person’s height is ruled by the length to which the longbones in the body finally grow. A condition called achondroplasiaprevents these bones from developing normally. People with thisinherited condition have a normal-size body, with a rather largehead, and legs and arms that are only half the length of normallimbs. They seldom grow to more than 4 feet (1.2 m) in height.

Growth

GROWING PAINS

Many children experience growingpains at some time or other,particularly between the ages of 8and 12. The pains are aches in thelimbs, particularly in the calf andthigh muscles. These mysteriouspains seem to be caused by theemotional stress of growing up,rather than by any physicalcondition. They are not connectedwith physical growth; for example, they do not occur more often attimes when someone is growingparticularly fast. Growing pains arenot caused by infections, allergies,or any other disease. Nervouschildren are more likely than othersto have growing pains. They occurmore often when the child is tired,particularly after exercise.

In time, children outgrow thesepains. While they last, the onlytreatment is a little rest andperhaps a mild painkilling drug. A child with severe pain in thearms or legs should be seen by adoctor, because that could indicatea more serious condition.

SEE ALSO

body systems • diet • food and nutrition • glands •puberty • skeletal system


101101

Hamstring injuries are common, especially among athletes, but they are not serious. The hamstrings are a group of threemuscles at the back of each thigh. Individually, they help twistthe leg in or out by rotating the knee. Together, the hamstringmuscles help bend the leg at the knee. These muscles are long,thin, and easily damaged. A hamstring may tear or becomebruised following a blow. Overstretched muscles can also tearwhen they are tired or are used without being warmed up. Thesigns of a hamstring injury range from a dull ache to a sharpshooting pain in the back of the thigh. Eventually, the musclegoes into spasm. Ruptured blood vessels can also cause swellingand tenderness in the muscle.

Prevention and treatmentThe best way to avoid hamstring injuries is to warm up beforeexercise by stretching the muscles. Fatigue increases the risk ofhamstring injuries, so it is also important to stop before getting

too tired. At the first sign of pain, the areashould be massaged, and the warm-upexercises should be repeated. A supportbandage may be necessary. If the paincontinues, all activity should be stoppedand medical help should be sought.

If a person suffers such an injury, he orshe should stop immediately. It may betempting to continue, but that only makesthe damage worse. The first thing to do is raise the leg and apply a compressionbandage to stop any bleeding. An ice packreduces swelling and inflammation.

Follow-up treatments includeultrasound massage to aid recovery. Heat and conventional massage helpdisperse blood clots and prevent internalscarring. Stretching exercises also help the muscle recover. Severe hamstringinjuries usually require pain relief.Crutches may also be needed to assistwalking. Hamstring injuries can takeseveral days to several months to heal.

Q & AA hamstring injury has kept meaway from football for a monthnow. I have been resting, so whyshould it take so long to heal?

Except in the first 24 hours, restis not the treatment for muscleinjuries. Once the bleeding intothe muscle has stopped, massage,heat, and exercise are the bestways to minimize the damagedone by bruising, and they willget the muscle back into shape.You really need to start aprogram of recovery now.

My brother has strained hishamstrings a number of times. Has he developed a weakness as a result of his injury?

Yes, probably, because an originalinjury was not treated properly.If your brother’s hamstringmuscles are treated adequately,there is no reason why theyshould not make a completerecovery. However, he needs to be careful to avoid over-stretching these muscles.

SEE ALSO

bruises • cramps • leg • ligaments • massage • muscle •physical therapy • sports injuries • sprains and strains

HamstringInjuries

The hamstring muscles are a group ofthree muscles that form the back of thethigh (the ham area) and span the femur(thighbone). They help bend the leg at the knee and twist the leg in and out.

hamstringmuscles

calf muscles


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Health foods, also known as whole foods or organic foods, aregrown and prepared in a more natural way than commerciallyprocessed food. They can be bought in health-food stores or in supermarkets but are often expensive because they are notmass-produced. Most food is treated in some way to make it last longer or look more appetizing. White bread, for example, is made from refined flour; the wheat germ and husk (bran),containing vitamins, minerals, and other health-giving substances,are removed during processing. Coloring, artificial flavoring, andpreserving agents are often added to food. Fruits and vegetablesare treated with pesticides and chemicals to help produce amaximum-yield crop from each plot of land. These food additivesand refining processes destroy much of food’s natural goodness.Experts believe that some of these treatments can be harmful to long-term health. Heart disease and some types of cancer, forexample, are linked with the consumption of too many refinedand treated foods. People are now buying more organic foodsthan ever before, because of the link with good health.

Health foods retain as much natural goodness as possible.Whole-wheat bread, cereals, and flours contain the wheat germand husk. Vegetable oils that are polyunsaturated, such as wheatgerm, corn, and sunflower oils, are known to be more healthfulthan saturated fats, such as butter or cream. Health-food storessell these oils unrefined, so they retain their nutrients, color, andflavor. Free-range eggs are preferable, because the hens are able to run freely outdoors, eating different foods. These scrapsprovide vitamins and minerals that are not usually present in

eggs from caged hens.Fruits and vegetablesavailable in health-foodstores are organicallygrown; manure or compostis used in the soil instead of artificial fertilizers, andpesticides are not used.

Q & AMy mother has always boughtus a commercial brand of peanut butter to put on oursandwiches. Now, one of myfriends says that it is not as good as the health store varietythat her mother buys. Is thistrue, or is it just a form of foodsnobbishness?

There is some truth in what your friend says. Commerciallyprepared peanut butter isusually homogenized; hydrogenis added, which destroys vitaminE and linoleic acid. Sugar is oftenadded, too. The peanut butterrecommended by your friend is made simply with groundpeanuts with, perhaps, a littlesalt and nothing else. It is alsomore nutritious.

What is all the fuss about whitebread? Isn’t it required by law toreach a certain nutritional value?

Yes, there are laws governing the production of white bread.However, only some of thenutrients removed from the flour during the refining processare put back in. White bread isnot as good a source of proteinas whole wheat bread, whichcontains wheat germ.

SEE ALSO

diet • dieting • food additives • food and nutrition •food labeling • minerals • vitamins

Health Foods

Whole-grain flour containsvitamins and minerals, much of which is removed from whiteflour during processing.

husk (providesbran fiber,minerals, and B vitamins)

endosperm(mostly starchand protein, usedin white flour)

germ (providesvitamin E and B vitamins)


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The heart is a large, muscular organ situated just above thediaphragm in the middle of the chest, although slightly more of it lies on the left side of the body than on the right. The heart’sfunction is to pump blood around two separate circulations, orsystems of blood vessels, in the body.

The body’s major circulatory system is called the systemiccirculation. It is a massive branching network of blood vessels—arteries, veins, and capillaries—to every part of the body and back to the heart. The heart pumps fresh blood filled withoxygen into the aorta, the central artery of the body. From there,the blood is distributed to the rest of the arteries. This bloodcirculates through the organs and tissues of the body, deliveringnutrients and oxygen to them. When all the oxygen has beenabsorbed from it, the blood is described as deoxygenated. Thisblood returns to the heart through the veins.

The heart then pumps the deoxygenated blood through itssecond circuit: this time a short journey to the lungs. This iscalled the pulmonary circulation, from the Latin word meaning“lung.” The lungs replace the used oxygen in the blood andremove the carbon dioxide that has accumulated in it. Thisoxygenated blood returns to the heart, and the circuit continues.

Structure and working of the heartThe pumping action of the heart is carried out by two pairs ofchambers (compartments): the left and right atria (which are the upper chambers) and the left and right ventricles (which liebelow the atria). Each chamber is a muscular bag, with a strong,muscular wall called the septum that divides the left and rightsides of the heart. The muscular walls of the chambers contractto push the blood along, and valves between the chamberscontrol the direction of the blood flow.

The heart powers both the pulmonary and the systemiccirculations in the following way. Blood flows through pulmonaryveins from the lungs into the left atrium of the heart. This bloodis rich in oxygen, provided by the lungs. The left atrium contractsand pushes the blood into the left ventricle. A valve between the left atrium and left ventricle ensures that the blood cannotflow back the other way. The left ventricle then contracts andpushes the blood out through another one-way valve into theaorta, and this major artery carries fresh, oxygenated blood to all parts of the body. On its return, the used blood has now lostits oxygen and flows into the right atrium of the heart, whichpushes the blood into the right ventricle. The right ventriclepumps this blood back to the lungs to pick up more oxygen, thuscompleting the double circulation. One-way valves ensure that

Q & ACan healthy people strain theheart through exercise in thesame way that they can pull a muscle?

No. In a healthy person, thisproblem would not happen.However, before people go for a long run, they shouldremember that “healthy” is not the same as “normal.”Coronary artery disease iscommon and may limit the work the heart can do. People in their forties and fifties arelikely to have some degree ofartery disease, and it is notunknown in younger people.Everyone should build up toexertion gently to avoid puttingthe heart under undue stress.People should also do warm-upexercises before they start.

When I get a shock, my heartfeels as if it will jump out of mychest. What causes this feeling?Is it serious?

Do not worry; your heart is quitenormal. The shock makes youradrenal glands pump outadrenaline, which suddenlydrives your heart to beat veryfast and forcefully, causing these symptoms.

Heart


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the blood flows one way only. With each heartbeat, the two atriacontract, followed by the two ventricles. When the body is at rest,this process is repeated between 50 and 80 times a minute.

Heart

Oxygenated blood from the lungs entersthe left atrium, passes to the left ventricle,and is pumped to the body via the aorta.Used (deoxygenated) blood from the bodyenters the right atrium via the vena cava.It passes into the right ventricle and thento the lungs to pick up new oxygen.

aortafresh blood to head and body

branch ofpulmonary artery

used blood to lungs

fresh blood from lungs

branches ofpulmonaryvein

valves

used bloodfrom body

superior vena cava

used blood to lungs

pulmonary valve



right atrium

left atrium

valve

right ventricle

left ventricle

aorta

inferior vena cava

used blood from body and legs

fresh blood to body and legs

SEE ALSOblood pressure • circulatory system • heart attack •muscle • oxygen • stroke


105

A heart attack occurs when the blood supply to the heart isobstructed. The coronary arteries are vessels that supply theheart with blood rich in food and oxygen. Heart attacks occurwhen these arteries become clogged with fatty deposits, acondition known as atherosclerosis. Blood clots can form aroundthe deposits and block the artery. In turn, that obstruction blocksthe blood supply to the heart. The person will then feel the chestpain that indicates a heart attack.

Warning signsA heart attack may come as a surprise, but most people get awarning. When the coronary arteries start to get blocked, theheart works harder during exercise or excitement. That maycause a crushing, suffocating pain in the chest, which mayspread to the arms and neck. Anyone who experiences this pain, called angina, should consult a doctor immediately.Smokers, diabetics, and those with a family history of heartattacks are most at risk.

Often, the main symptom of a heart attack is a severe pain in the chest. The pain is usually more acute than angina; it may be so severe that the person collapses.

In some cases, there is little pain and the person may mistake the heart attack for indigestion or heartburn. Othersymptoms include sweating, shortness of breath, and a weak or slow pulse.

Diagnosis and treatmentA heart attack is a life-threatening condition. It requiresimmediate hospital treatment. In the hospital, doctors confirmthe heart attack with blood tests. An electrocardiogram (ECG)may be given to monitor the electrical activity of the heart. In this procedure, the heart’s tiny electric currents are recorded on a machine called an electrocardiograph, which prints out theresult—the ECG—on a roll of paper. Any heart disorder, such as a heart attack, shows up as a change of pattern.

Morphine is usually given as pain relief. More drugs may begiven to improve the circulation and limit damage to the heartmuscle. If there are no complications, most patients can returnhome to rest after a week or so.

Q & AIs there anything I can do now to prevent a heart attack fromoccurring in later life?

Do not smoke. Smokingsignificantly accelerates the pace of atherosclerosis (thehardening and thickening of the artery walls), which is the cause of coronary arterydisease, and it is thus a mainfactor in heart attacks. There is also strong evidence that if you eat less food that containssaturated fats (which are mostlyof animal origin, such as butterand cream), you can reduce the risk that your coronaryarteries will become narrowedby cholesterol deposits. Aerobicexercise in the form of running,cycling, and swimming may also help.

My father, who has always led an extremely active life, has just had a heart attack. Does this mean that he will have to slow down now?

Not necessarily, unless he hasbeen told to do so by his doctor.Your father should avoid suddenbursts of activity, however, andbuild up to any exertion moregradually than he did before.

Heart Attack

SEE ALSOblood pressure • circulatory system • heart • oxygen •pain • stroke


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The body temperature is normally about 98.4°F (37°C). If thesurrounding temperature rises, the body’s thermoregulationsystem reacts: it stops the body from overheating and protectsthe brain, which cannot tolerate high temperatures. The bodyreacts in two ways. Its main reaction is to perspire. As the sweatevaporates, the skin cools. The body can also lose heat by thedilation of blood vessels; when they widen, more blood reachesthe skin, which takes on a flushed appearance, and the bloodcools. Sometimes, the body is badly affected by heat. Heat cramps,which are caused by physical effort in extremely hot conditions,are an occupational hazard of miners and firefighters.

In the condition called heat exhaustion, or heat prostration,victims may collapse as a result of excessive loss of fluid and salt. Victims sweat so much that their body temperature remainsnormal. In very hot, damp places, however, the sweat may notevaporate and cool the body. Heatstroke—or sunstroke—mayoccur; in this condition the patient’s temperature rises rapidly.This is a very serious condition that can lead to permanent braindamage and even death. People who move from a cool climate to a hot one are at risk of heat exhaustion or heatstroke.Outdoors, they should wear light clothes and a sun hat andshould be careful not to sunbathe or exercise for too long. A lotof fluid is lost during perspiration; this fluid has to be replaced by taking extra liquids and salt. Anyone who shows signs of heatsickness should be taken to a cool place as soon as possible andgiven salty water to drink.

Q & AWhat is the difference betweensunstroke and heatstroke?

There is no difference. Bothterms describe the serious and potentially fatal conditionthat can occur if the body isexcessively heated, resulting in the total breakdown of the temperature-regulatingmechanism in the body.Heatstroke is a more accuratename, because you can sufferfrom its effects away from thesun. If the temperature is highenough, you can get heatstrokeeven when not in direct sun.

Heat Sickness

When the body is cold (left), the blood vessels narrow, less sweat isproduced, the hair stands straight out from the skin, and goose bumpsdevelop. When the skin is heated (right), the blood vessels dilate, the sweat glands work harder, and the hair lies closer to the skin.

SEE ALSOdrinking water • exercise •salt • skin • sunburn • sweat

sweat gland

goose bump

blood vessels

sweat droplets

hairshaft

dilatedbloodvessels


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A hernia is a bulge of soft tissue that forces its way through an opening or weak place in the surrounding muscles and fibrousconnective tissues. If it is an external hernia, the bulge of tissue is covered with a layer of fat and skin. The bulge usually containseither a loop of small intestine or part of the fatty membranethat covers the intestines. Hernias most often appear in theabdomen. A hiatal hernia, for example, is formed when part ofthe stomach pushes up into the chest through a weak place inthe diaphragm. Other hernias may occur in the groin (inguinal orfemoral hernia) and near the navel (umbilical hernia). Herniasmay be caused by straining the muscles while doing heavy workor by allowing muscles to become weak through lack of exercise.

Symptoms and treatmentSome hernias produce no symptoms, but those near the surfaceof the abdomen may cause a tender lump, which disappearstemporarily when pressed. A hiatal hernia may allow food andacid to move from the stomach back into the gullet. That causesa burning pain behind the breastbone. Sometimes, the bloodsupply to the hernia may be totally cut off. When this happens,the tissues within the bulge swell, die, and decay. This conditionis known as a strangulated or incarcerated hernia. It is extremelypainful and needs an immediate operation.

Most hernias need to be treated by surgery. The bulging tissueis pushed back into place and the defect repaired. This is usuallya fairly simple surgical procedure carried out in a hospital. Thesymptoms of a hiatal hernia can be eased by losing excessweight, taking antacids, and eating small, frequent meals.

Q & ADon’t hernias hurt? My uncle has a hernia, but he says he’s not in pain.

Hernias do not usually hurt,except when they first occur—for example, during heavy lifting. Afterward, they may be a bit uncomfortable, but they are usually not painful. If a hernia does hurt, it may be strangulating because itsblood supply is cut off; medicaladvice should be sought.

Can a tendency toward herniasrun in families?

Yes, but there is no definitehereditary link. Members ofsome families tend to do the same types of jobs—forexample, those involving heavylabor, which are more likely tocause a hernia.

Hernia

Groin or inguinal hernias are extremelycommon. They occur more often in menthan in women. The soft lump bulgeswhen the patient coughs but disappearswhen he lies down. This type of herniacan be treated by wearing a truss or by a simple surgical operation.

abdominal muscle

intestine

fat

SEE ALSOdigestive system • digestive system diseases and

disorders • muscle • respiratory system


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The hips are the largest and strongest joints in the body. Theycarry all the body’s weight and enable a person to stand, walk,and run. A hip joint is literally a ball-and-socket joint. The ball ofthe joint is a projection on the end of the femur (the thighbone).It fits into the socket, which is a cup-shaped hollow in the iliacbone. The iliac bone is part of the pelvis.

The hip joint is padded with cartilage and fatty tissue andlubricated by a special fluid. Tough ligaments hold the joint inposition and prevent the ball from slipping out of the socket.Muscles lying over the ligaments enable people to move theirlegs in many different positions.

In some newborn babies, the hips slip out of joint easily. This problem requires immediate treatment. In some elderlypeople, the joint may wear out. It can usually be replaced by an artificial joint made of stainless steel and plastic.

Hip

An artificial hip can replace a badlyfractured one. This artificial hip(above) is made of stainless steel and titanium.

The hip is a ball-and-socket joint. Thecartilage that covers the head of thefemur ensures smooth movement. The joint is lubricated by special fluidproduced by membranes. Ligaments hold the hip in position, and pads of fat help cushion the joint, acting as shock absorbers.

fractures and dislocations • joint disorders • joint

replacement • joints • leg • ligaments • skeletal system

SEE ALSO

pelvic girdle

ligamentsurroundinghip joint

femur (thighbone)

ligaments

pad of fat

pelvic girdle

iliac bone

cartilage

femur


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Homeostasis is the mechanism that keeps a body’s systemsstable and in balance. The human body is a complex machinewith many control systems that keep it running smoothly. The body works best if its internal conditions are kept more or less the same all the time. The way the body keeps things the same is called homeostasis, meaning “same” and “still.”Homeostasis helps maintain the right amount of water or saltsin the body, keeps the body at a certain temperature, and makessure that the body is operating at the correct rate for whatever a person is doing at any one time.

Homeostasis in actionSince homeostasis happens automatically, people do not have to think about it, but they can still see when it is happening. For example, when a person exercises strenuously, the musclespowering the legs and arms produce heat. This heat increasesthe body temperature. If that process was allowed to continue, it would soon get too hot for the body to function properly.Detectors throughout the body sense the temperature increaseand tell the homeostatic system to cool down the body.

These homeostatic messages are sent around the body via thenetwork of nerves and by chemical messengers called hormones.Nerve signals make sweat glands pump water onto the skin tocool the surface of the body. Other glands produce hormones,which make the blood vessels in the skin expand, so the skinbecomes red as it fills with blood. That helps heat in the bloodescape from the body. When the body is cold, however, bloodvessels in the skin constrict (become narrower), making the skin pale as blood moves into the middle of the body, and heat is prevented from being lost to the outside.

Negative feedbackHomeostasis works by the principle of negative feedback: If onecondition changes, a negative-feedback system works to bringthat condition back to how it was before the change took place.For example, if the amount of water in the body gets too low, a negative-feedback system operates to increase the water levelby making the person feel thirsty, so that he or she will drinksome water. If the water level gets too high, negative feedbackreduces the level by making the person urinate.

Q & AI’ve heard that hunger is part of a homeostatic mechanism. Is that true?

Yes. Hunger is induced whenbrain cells detect low levels of blood sugar (glucose) andemptiness in the stomach. Thesensation of hunger prompts the individual to seek and eatfood. If this is successful, theblood sugar rises and the stretchreceptors in the stomach signalthat no more food is currentlyrequired.

Homeostasis

Feeling thirsty is an example ofhomeostasis in action; the body’smechanisms have detected that the level of water is too low, and a negative-feedback system initiates thirst.

SEE ALSO

body systems • drinking water • exercise • glands •nervous system • salt • sweat


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Hyperventilation is a syndrome (a collection of symptoms)usually caused by anxiety. It may also occur during panic attacks.Anxious people sometimes feel as though they cannot getenough air into their lungs. As a result, they breathe too rapidlyand deeply, lowering the level of carbon dioxide in the blood.Consequently, they feel dizzy and have numb and tingling handsand feet. Their fingers and toes may also go into a painful anduncontrollable spasm.

Some people hyperventilate if they experience pain. Thequickest cure is for the patient to breathe into a small paper bag for a few minutes. The carbon dioxide breathed out is thenbreathed back into the lungs. Once people realize that they have been hyperventilating, the problem usually stops.

Q & AOnce, after I received some bad news, I noticed that I wasbreathing quickly and had atingling sensation around mymouth. What caused this?

Hyperventilation, or fastbreathing, occurs in some people when they are upset.Hyperventilation causes anabnormal loss of carbon dioxide,a change in blood acidity, and a consequent drop in bloodcalcium. Nerves require calciumion movement for properfunction, and this is why your nerves were affected.

I’m a little nervous, and I findthat I get breathless sometimes.When this happens my fingersstart to tingle, and once myhand cramped. What causesthese problems?

You have a complaint that iscommon among nervous people.It is called hyperventilationtetany and is harmless.Treatment is simple; you should breathe into and out of a paper bag for a fewminutes. That will bring thecarbon dioxide in your bloodback to its correct level and your hand will return to normal.

Hyperventilation

asthma • cramps • nervous system • oxygen • pain

SEE ALSO

Hyperventilation can easilybe cured by breathing into a paper bag. That increasescarbon dioxide levels in the blood and restoresbreathing to normal.

NF_MC Bind_Up_pp84-123.qxd:Nutrition And Fitness 5/24/10 9:48 AM Page 110

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Sprains and strains, bruising, and bleeding can all be treated by cooling the injured area with ice. This treatment causes theblood vessels to contract and slows down or stops the bleeding,reduces swelling and inflammation, and helps relieve pain.Applying an ice pack is a quick and efficient way of dealing with many playground and sports injuries.

Making an ice pack is easy. Some crushed ice should be sealedin a plastic bag, which is then placed inside a damp cloth. Thecloth should be tied up securely and held gently but firmly overor around the injured area for about 10 minutes. If possible, theinjured part of the body should be elevated and rested beforeand during application of the ice pack. A sterile dressing shouldbe placed over any open wound or scrape before the ice pack is applied. An injured joint should be exercised as soon as the ice pack is removed, to prevent it from becoming too stiff.

Q & AI cut my lip recently, and it bled alot for such a tiny wound. Why?

The lips are richly supplied withtiny blood vessels; thus even a small cut can result in muchbleeding. Rubbing the cut withan ice cube will constrict theblood vessels, help the blood toclot, and help relieve the pain.

Why does an ankle swell somuch if it is sprained?

A minor twist of the ankle whenit is bearing the body’s weightcan result in severe damage tothe ligaments that support it.Fluid leaks from the damagedblood vessels into the tissues,and bruising may occur. Theswelling can be reduced by usingice to constrict the blood vessels,elevation, and compression withan elasticized bandage.

Ice Therapy

Making an ice pack: (1) Place theice in a plastic bag and crush itwith a mallet or hammer. Thatallows the pack to contoursmoothly to a rounded part ofthe body. (2) Tie up the bag ofcrushed ice in a damp cloth,which protects the skin fromfreeze burn. (3) Apply the pack forabout 10 minutes. Any longerthan this can burn the skin.

1

2 3

USES FOR ICE PACKS

Ice packs can be used briefly, andwith care, to help bring down afever. Ice packs are also used insports clinics and physical therapydepartments to relieve pain beforeand during a session to exercise aninjured muscle.

SEE ALSO

bruises • circulatory system • sports injuries • sprains

and strains


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Indigestion is pain or discomfort in the upper abdomen thatusually occurs after eating, particularly if the meal includes rich, spicy, or fatty foods. It can occur as a sensation of fullness or nausea, as a gnawing or burning pain, or as a dull ache in the chest, which is sometimes called heartburn. Some peopleexperience an unpleasant acidic taste in the mouth if indigestioncontinues for some time. The tongue may become dry andcoated, and the breath becomes stale.

When the body digests food, the muscles of the stomachsqueeze regularly to crush the food. The lining of the stomachproduces enzymes and acids, which break the food down further.Then the food passes to the duodenum, where more enzymesdigest it before it moves into the intestine. When the stomach is empty, its muscles relax and the lining stops producing theacids and enzymes. The symptoms of indigestion are caused when food remains in the stomach for longer than usual and when substances irritate the lining of the stomach andduodenum. All sorts of items can cause indigestion, among themcucumbers and pickles, creamy dishes, highly spiced foods,caffeine, and alcohol. Eating very quickly, being overweight, andsmoking increase the risk of suffering from indigestion. Manypeople get indigestion when they are stressed or when they takedrugs, such as aspirin, that can irritate the digestive tract.

Everyone has indigestionfrom time to time. If ithappens very often, lastsfor a long time, or is very severe, it may be a symptom of a moreserious stomach disorder,and a doctor should beconsulted.

Q & AMy father often gets indigestionafter he eats a big meal.However, he likes to eat, so what can he do to prevent the indigestion?

The most common causes of indigestion are eating late in the evening, eating spicy or rich foods, eating too much, and drinking alcohol. If yourfather eats slowly and missesone of the courses, he should be able to reduce his indigestion.If possible, your father shouldallow at least two hoursbetween eating and his bedtime.

SEE ALSOdiet • digestive system • digestive system diseases and

disorders • food and nutrition

Indigestion

Eating too quickly is one ofthe easiest ways of gettingindigestion. It is best to sitdown calmly and chew foodslowly to aid digestion.Eating when on the moveshould be avoided.

AVOIDANCE ANDTREATMENT OF INDIGESTION

Avoid indigestion by• Eating regularly and slowly• Chewing food well• Getting plenty of exercise• Eating plenty of fiber to avoid

constipation• Avoiding heavy drinking• Avoiding or reducing spicy foods,

greasy foods, and caffeine

Treat indigestion by• Taking an antacid• Sipping water and sitting in a

cool place, or walking around


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The tiny amounts of iodine that the bodyneeds to function properly are usuallyprovided by foods such as sea fish,shellfish, and sea salt.

Iodine is a mineral essential for good health, and it is also anecessary component of the hormone thyroxine, which is madein the thyroid gland. Thyroxine is responsible for growth anddevelopment and helps maintain the body’s vital life-supportprocesses, such as body temperature, use of oxygen, anddigestion. If the body produces too much thyroxine, theseprocesses speed up. If too little thyroxine is produced, they slowdown. Lack of iodine in adults causes the thyroid gland toenlarge, a condition known as goiter. Myxedema is anotherdisorder caused by lack of iodine. Patients suffering frommyxedema become very slow in their actions and gain weight.Their speech and thoughts also slow down. Diseases due to lackof iodine are rare in the Western world.

The body needs only tiny amounts of iodine. Sea salt, fish, andother seafoods are the best sources. Iodine was also once widelyused as an antiseptic to clean infected skin.

Q & AWhy do people who live incertain geographical areas seemparticularly prone to goiter?

A goiter is a swelling of thethyroid gland. This gland needs a supply of iodine from food orwater to produce its hormone,thyroxine. If there is a deficiencyof iodine, the thyroid swells. Thistype of goiter is called endemicgoiter. Certain areas of the world,particularly inland mountainregions, lack iodine in the soiland water, so the inhabitantslack iodine, too. In such areas,one must use iodized table salt.

My aunt was given radioactiveiodine for an overactive thyroidgland. Was this radiotherapy?

Yes. Unlike other parts of the body, the thyroid glandselectively stores iodine. A drinkof radioactive iodine is given tothe patient, and the amount ofradioactivity that passes into the thyroid gland is sufficient todestroy overactive tissue withoutharming other parts of the body.

SEE ALSOdiet • glands • growth • minerals • nutritional

diseases • salt • skin

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Many youngwomen suffer fromiron-deficiencyanemia at sometime in their life,because of bloodloss duringmenstruation.However, the bodycan store iron, andif women eat ahealthy diet ofanimal foods andgreen vegetables,they can avoidanemia. Ironsupplementsshould not betaken unless adoctor prescribesthem. Taking toomuch iron candamage the liver.

anemia • minerals • nutritional diseases • vitamins

SEE ALSO

Iron is a mineral that, together with protein, produceshemoglobin. Hemoglobin is a pigmented protein in the red bloodcells that transports oxygen from the lungs to the body tissuesand gives red blood cells their color. The body does not make iron;it obtains iron from food. The average adult body contains about0.1–0.14 ounce (3–4 g) of iron. Some of this iron is stored in theliver and spleen; the remainder is present in the red blood cellsand in the bone marrow.

Lack of iron in the diet causes anemia, which is one of themost common deficiency disorders in women. An anemic personis constantly tired and unwell. Treatment involves extra ironsupplements. Pregnant women need extra iron, as the growingfetus draws on the mother’s supply. Although liver, legumes, milk,eggs, wheat germ, and leafy green vegetables are all goodsources of iron, large doses of vitamin A have been linked to birthdefects, so liver and its products, which contain high levels of thisvitamin, should be avoided during pregnancy.

Q & A

Iron

Do you lose iron if you giveblood regularly?

Yes. If you give blood once everythree months, you lose abouttwice as much iron as normal,but a good mixed diet willreplace the loss.

Is it true that spinach contains a lot of iron?

Spinach contains around 0.00012ounce (4 mg) of iron per 3.5ounces (100 g) of spinach, whichis a moderate amount. Unrefinedflour and dried peas and beanscontain more iron than mostgreen vegetables, as does meat.The iron in meat is also moreeasily absorbed by the intestinethan the iron in vegetables.

Is it true that iron pills aredangerous for children?

Iron can cause poisoning ininfants and children, who shouldtake iron supplements onlyunder strict medical supervision.It is unusual in the United Statesfor children to be given iron pillsto treat an iron deficiency. Adoctor is more likely to suggestincreasing the amount of iron-rich food in the child’s diet.


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Irritable bowel syndrome is a common disorder that featuresabdominal symptoms for which no organic cause can be found.In the past it was given other various names, such as nervousdiarrhea, spastic colon, or idiopathic diarrhea. The term idiopathicsimply means that the cause is unknown. In the United States,about half the patients seeking medical attention for bowelupset are suffering from irritable bowel syndrome.

Symptoms The condition usually develops between the ages of 20 and 30and is twice as common in females as in males, but people of anyage and of both sexes can suffer from it. Symptoms are variedand tend to be intermittent. Some pain in the abdomen is usual.Recurrent episodes of pain are commonly localized in one of thefour corners of the abdomen and may be relieved by emptyingthe bowel. The pain may start soon after eating, and manysufferers are convinced that it is brought on by a meal. Eatingalso often induces an urgent need to use the toilet.

Diarrhea is common and often alternates with constipation,but the condition may involve unduly frequent, but otherwisenormal, bowel motions. There may be a constant sense ofabdominal fullness and an awareness that something ishappening in the intestines. The sufferer is conscious ofabdominal noises (borborygmi) and excessive gas production(flatus), and there may be nausea and headache. Sometimes,there is a feeling that there is incomplete emptying of the bowel.Sufferers often notice that the stools are small and rounded oroccasionally ribbonlike. Stools may also contain visible mucus. A common feature of the syndrome is anxiety about intestinalfunction and other health matters.

Normal movement of the bowel contents is brought about by a process known as peristalsis. This is a continuous processorganized by a network of nerves in the wall of the intestine,which involves automatic tightening and relaxation of shortsegments so there is a progressive shifting of the contents in the direction of the rectum. Healthy people are rarely aware ofperistalsis, but people suffering from irritable bowel syndrome are acutely conscious of it. This is partly because peristalticcontractions are stronger and more frequent than normal andpartly because there is undue awareness of body function.

CausesPeople with irritable bowel syndrome are often convinced thatthey are allergic to certain kinds of food, and that this is thecause of the problem. Food allergy, however, is far less common

Q & AMy sister always has diarrheaand stomach pains beforeexams. Does she have irritablebowel syndrome, or is this justher nerves acting up because of the exams?

Many people have this kind of reaction before exams. Thewhole nervous system isaffected, and this causes theintestine to become overactive.An irritable intestine causes asimilar kind of spasm, but it lastsmuch longer and may arisewithout obvious stress.

My doctor thinks I may haveirritable bowel syndrome, and he wants me to go to thehospital to have some testsdone. I don’t like medical tests.Are they really necessary?

There are no symptoms thatpositively distinguish irritablebowel syndrome from othertypes of bowel disorders.Diagnosis has to be made byexcluding other possible reasonsfor your symptoms. This can bedone only by hospital tests. Itdoes not mean that your doctoris expecting to find anythingserious, but having the testsdone will provide reassurance.

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than is generally supposed, and most doctors do notaccept this theory. The syndrome invariably has eithera psychological basis or a strong psychologicalelement. It is notoriously common in women of highintelligence and driving ambition, especially thosewith a tendency to tension and anxiety aboutprofessional, financial, and family matters. Thesyndrome often starts after a life crisis or a period of emotional stress. Many sufferers have developedirritable bowel syndrome after a divorce or abereavement. In some cases, there is a strong, but not always realized, fear of cancer.

Diagnosis and treatmentDoctors recognize that it can be a serious error to make a premature diagnosis of irritable bowelsyndrome without full investigation. Beforeconcluding that a person’s symptoms are due entirelyto irritable bowel syndrome, it is necessary to excludea number of other possibilities by carrying out sometests. One of the most important of these is a bariummeal X-ray. Barium is an element that X-rays cannotpass through, so it is used to outline internal organs.

In irritable bowel syndrome, a barium meal X-ray shows nostructural abnormality, but it may indicate an unusual degree of contraction of the circular muscle fibers of the bowel. Thissuggests that the colon is in a state of abnormally high activity.

Some people with irritable bowel syndrome may require drug treatment to relieve their underlying anxiety. Carefulexamination to exclude an organic cause, followed by strongreassurance, is often enough to provide a cure. A diet high invegetable fiber is also helpful in regulating bowel activity. Anumber of drugs have a specific sedative effect on peristalsis.These calm down excessive contractions in the intestine andrelieve abdominal pain.

If patients have psychological symptoms, such as anxiety, thedoctor may refer them to a therapist, who can give advice onhow to alleviate stress. Some people learn to use mind and bodyrelaxation techniques to help reduce their stress and so improvetheir bowel symptoms.

The larger blue structure shows a normalcolon; the red one depicts the distensionand constriction that is common inirritable bowel syndrome. Musclemovement in the red colon is shown in yellow, and arrows show the directionof the flow of feces.

Irritable Bowel Syndrome

SEE ALSO

constipation • digestive system • digestive system diseases

and disorders • pain


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exercise • jogging • muscle • physical fitness • yoga

SEE ALSO

For one type of isometric exercise, lie on the back with the knees bent.Push the feet firmly against the floor, raise the body (left), and bring thearms to knee level and beyond (right). Count to six, relax, and repeat theexercise 10 times.

Isometric exercises are a good way to build up muscle over aperiod of time. They are performed against an immovable objectsuch as a floor, wall, a desktop, or even a fist. Different exercisesdevelop the strength of particular sets of muscles, such as thechest, upper arms, or thighs. The advantage of isometrics is thatthey can be done anywhere—in the car, at a desk, or wherever aperson happens to be. People need to work on the exercises foronly about two minutes per day. After about four or five weeks ofregular exercise, they will be able to measure the increase in sizeof the muscles worked on. However, isometric exercises do nothelp with general physical fitness unless they are combined withother types of exercise that involve the whole body, such asbending, stretching, cycling, and jogging.

PilatesPilates is an exercise method developed by Joseph Pilates(1880–1967) to improve physical and mental health. This methodfocuses on building the body’s core strength (back, abdominal,and pelvic muscles) and improving posture through a series oflow-repetition, low-impact stretching and conditioning exercises.The aim of Pilates is to provide a complete body workout anddevelop an awareness of how the body works, enabling the mindand body to work in harmony. Pilates is based on eight principles:relaxation, alignment, control, precision, routine, breathing,centering, and flowing movement.

IsometricExercises

Q & AMy boyfriend plans to useisometrics to build large biceps.How long should it be beforethere is an improvement?

If your boyfriend does isometricexercises properly, he shouldprobably be able to feel andmeasure a change in all themuscles involved after fourweeks. However, to achieve thefigure of a bodybuilder takesmany months of intensive workat isometric exercises, combinedwith weight lifting and otherfitness routines.

I am a football player. Would it help to do some isometricexercises as well as jogging as part of my training?

Yes. Isometrics will help you todevelop specific sets of musclesthat need to be very strong foryour sport.

I would like to become fit. Areisometrics enough?

No. Isometrics are only forbuilding up the muscles. They do not improve the condition ofyour heart and lungs—one ofthe main objects of most formsof exercise.


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Jogging is a popular form of exercise, and if done properly, it can beextremely good for people. The time spent jogging should be built upgradually. Joggers should move at a slow pace, with their whole body,particularly the shoulders, relaxed; comfortable clothes and rubber-soledrunning shoes should be worn. Joggers should not go too fast—a goodtest is to be able to talk with a friend as they jog.

Jogging is a form of exercise that involves running at a slow,steady pace. It is a popular fitness activity for people of all agesthat can be done anywhere and at any time. It does not requirespecial training or the use of special sports facilities. All that isneeded is a road, track, park, or lane where people can run insafety. Even city dwellers do not usually have a problem fittingjogging into their daily routines. Many men and women, forexample, jog to and from work every day or take a daily jogaround a local city park. Parents and children often take an earlymorning jog together.

The benefit of jogging is that it is an aerobic exercise, whichhelps the body use oxygen more efficiently and strengthens the cardiovascular system (heart, lungs, and circulatory system).Jogging and other aerobic exercises make the heart larger andstronger and, therefore, less prone to disease. Lung capacity is increased, so people are less likely to get out of breath.Metabolism also improves so that waste products, toxins, andexcess fat are removed more easily. All this makes people fitterand stronger.

Jogging guidelinesBeginners and overweight people should start jogging gently,building up their fitness gradually. A sensible way to begin is bycombining walking with jogging in 15-minute periods. The personthen gradually cuts down the walking periods until eventually heor she is jogging for the entire time. It is important to run at aslow, steady pace to exercise the heart and lungs properly. Ifpeople jog at a speed at which it is uncomfortable to talk with a friend, they are going too fast. Most adults should have amedical examination before they start to jog. As long as theybegin gently, there is very little risk. However, older people whohave not exercised for a long time or people with heart problems may be at risk. They should see their doctor before jogging.

Q & AMany of my parents’ friendsseem to have taken up jogging.Why is it considered such a greatfitness activity?

It may seem strange that manypeople jog as though their lifedepends on it. Yet a person’s lifemight really depend on jogging,or at least on taking exercisethat uses the heart and lungs.Jogging helps to counteract theeffects of many things, includingstress and a high-fat diet, thatcontribute to heart disease.

SEE ALSOaerobics • basal metabolism • diet • exercise • heart •physical fitness • sports • sports injuries

Jogging


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The joints undergo a great deal of wear and tear, so it is notsurprising that they suffer from a number of disorders. Somedisorders are easily cured with treatment and time, but othersmay need surgery. Sprains and strains caused by awkward oraccidental movements and falls are the most common injuries tojoints. They cause swelling and may be extremely painful. Theseinjuries are treated with bandaging and rest of the affected limb.

Knee joint disordersThe knee joint is often injured in sports when it is accidentallytwisted and wrenched. It contains two floating pieces ofcartilage, which may be torn or crushed. Such an injury causessevere pain and sometimes stops the knee from bending. If thishappens too often, the cartilage may have to be removed. Intime, the muscles of the knee grow strong enough to take theplace of the cartilage.

Sometimes, the whole knee swells after an injury, a conditioncalled water on the knee. Like many other knee problems, it clearsup with rest. Too much kneeling on a hard surface or a blow tothe knee may cause one of its soft lubricating pads, or bursae, to become inflamed. In this disorder, known as bursitis, orhousemaid’s knee, a painful, fluid-filled swelling develops in frontof the kneecap. Other joints where bursitis may develop includethe elbow, the heel, and the base of the big toe.

DislocationsAccidents may also lead to dislocation, when one bone of a jointis wrenched out of its socket. This displacement prevents normalmovement of the joint and is usually extremely painful. Themuscles, nerves, and blood vessels around the joint are damagedand the tissues swell. Skilled treatment is needed to repositionthe bone as quickly as possible. The shoulder, jaw, and hip areparticularly likely to be dislocated.

Spinal joint injuriesThe joints of the spine are often injured. The spinal bones(vertebrae) are joined by fibrous tissue. Small disks of pulpymaterial surrounded by rings of fibrous tissue act as shockabsorbers between vertebrae. When the vertebrae are crushedtogether, as in heavy lifting, the pulp may be forced through the fibrous tissue and press against the spinal cord or a nerveroot. This condition is known as a slipped, or prolapsed, disk andcan be very painful. Symptoms may come on suddenly or over a period of time. Treatment includes bed rest (lying on a firmmattress for support) and taking painkillers.

Q & AI dislocated my right shoulder a few months ago. Now itdislocates easily, and I have hadto give up playing football. Isthere anything I can do tostrengthen the joint?

It is possible to have anoperation, known as the Putti-Platt operation, to increase the strength of the joint if ashoulder repeatedly dislocates.This procedure builds up thebone at the front of the shoulderto increase the depth of thesocket, making it more difficultfor the bone to slip out. Healingtakes about two months.

I am double-jointed. Am I morelikely to develop rheumatismwhen I get older?

People who are said to bedouble-jointed do not, in fact,have double joints. They do havegreater than normal flexibilityand can move their bodies andlimbs through a wider range ofmovement than most people. As a result, their joints aresubjected to unusual stressesand strains through overuse.“Double-jointed” people may be more prone to aches andpains in their joints later in life.

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Other joint disordersInflammation of the synovial membrane that lines a joint can becaused by an injury or by rheumatoid arthritis. Sometimes, it canlead to ankylosis, or permanent fixation of the joint. This mostoften affects the area around the spine and the pelvis. The jointsmay also be affected by osteoarthritis, which causes the cartilagearound them to wear away gradually.

People whose joints are badly worn away, creating pain andlimiting movement, can now be fitted with new joints made ofmetal, plastic, or ceramic. These artificial joints help relieve thepain, and, with exercise and practice, the patient may, in time,regain full movement of the joint.

RheumatismRheumatism is a term used to describe a range of aches andpains. It is not a disease in itself; it is more a collection ofsymptoms. The aches and pains, including swelling, tenderness,and stiffness, affect the joints and other surrounding structures,such as muscles, tendons, and ligaments.

Joint Disorders

Highly mobile joints, which include theelbow (top left) and the knee (bottomleft) are particularly susceptible to injury.These joints are enclosed within fibroustissue, known as the joint capsule, andcontain synovial fluid, which acts as alubricant. The knee joint also containsshock-absorbing cartilage pads. Certainjoints on each of the ribs (top right),however, are formed from bone andcartilage. These cartilaginous joints allowmovement without the need for fluid-filled synovial membranes, as in theelbow and knee.

synovial fluid

breastbone, or sternum

ribs

flexiblecartilage at jointsallows ribmovement

spinecartilage pad

smooth cartilageon bone endslessens friction

joint capsuleELBOW RIB CAGE AND SPINE

KNEE

SEE ALSOarthritis • elbow • fractures and dislocations • hip

• joint replacement • joints • knee • leg • ligaments •muscle • muscle diseases and disorders • shoulder •skeletal system • sports injuries • sprains and strains

• tendon


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Joint replacement refers to a type of operation in which adiseased or damaged joint, such as a knee, is removed andreplaced by an artificial, or prosthetic, joint. In the past, peopleoften became less mobile as they aged, because accumulateddamage to the joints caused so much pain that they could notbear to move. However, joint replacement has given many peoplethe ability to enjoy an active life well into their senior years.

Joints are structures where two or more bones, bone andcartilage, or bone and teeth come together. They are usually heldtogether by a series of muscles, ligaments, and tendons. Somejoints allow no movement; others allow movement to a greateror lesser degree. Joints that allow a significant amount ofmovement often include layers of cartilage between the bones to prevent them from grinding against each other. They are alsooften enclosed within sacs filled with fluid to lubricate andcushion the joint to ease movement.

Joints that allow movement are the ones subject to thegreatest wear and tear over the course of life. Not surprisingly,they are the ones that are most often replaced. Hip, knee, andankle joints top the list of those that are replaced, because oftheir importance in walking and in supporting the weight of thebody. Other joints that are frequently rebuilt include the shoulderand the many joints in the hand and wrist.

Damage to the joints can result from overuse, injuries, failureto heal properly after an injury has occurred, or from chronic orinfectious diseases. Arthritis, old age, obesity, and repetitive stressall contribute to the need for joint replacement.

The procedureJoint replacement is often a last resort; medication and physicaltherapy are less drastic and less risky treatments for joint pain.However, when joint damage is so severe that pain cannot bemanaged or when it is so severe that it limits the daily activitiesof the individual, surgery becomes a more desirable option.

During surgery, the damaged or diseased bone and cartilageare removed. The affected area is cleaned out and prepared forinsertion and attachment of the prosthesis (replacement joint),which is made of metal, plastics, ceramics, or some kind ofcomposite material. The muscles and tendons are then attachedto the prosthesis, and the site is closed.

After surgery, the joint is immobilized for some time to avoiddamage to the prosthesis as well as the remaining tissue.Inflammation, a natural response to injury, must be controlled toprevent swelling of the tissues, which restricts the blood supplyvital to the healing process. Pain also has to be managed.

Q & A

JointReplacement

When a joint is replaced, is thenew joint from a human donor?

No. Replacement joints arealways artificial.

Which joints can be replaced?

Most replacement operationsinvolve the hip and the knee.However, joints have beendesigned for the finger and toejoints; the elbow, shoulder, andankle; and the articulation of thejaw (the temporomandibularjoint in front of each ear).

Do artificial joints last for a lifetime?

That depends on the recipient’sage. Many new joints performwell for the rest of a person’s life,but loosening of the attachmentto the bones and other problemssometimes occur. Such problemsmay require a further operation.

What does a joint revisionoperation involve?

Joint revision involves openingup the joint site, removing anyloose or damaged artificial parts, and replacing them withnew parts.


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This X-ray of the knee shows a side view of an artificial replacement. Thecomponent parts of the new joint arefixed into the femur, or thighbone, andthe tibia, or shinbone.

Taken after a hip replacement operation,this X-ray shows a metal componentscrewed into the femur (thighbone) tostrengthen it. (The zipper and buckle ofthe patient’s trousers appear at the left.)

Once the patient is well enough, physical therapy and trainingare very important, because the person must learn how to liveand move with an artificial joint. Appropriate exercise increasesthe strength of surrounding muscles and promotes healing byincreasing blood flow to the site of the operation.

Potential complicationsJoint replacement surgery is not without risk. Patients who havetheir hips, knees, or ankles replaced are at increased risk of bloodclots. That can lead to potentially fatal complications, such aspulmonary embolisms (in which the blood clot comes loose andis transported to the lungs). Infections are always a potentialcomplication of surgery, as is excess bleeding or pneumonia.Prostheses may become displaced from their proper position ormay break free entirely. Abnormal bone growth adjacent to theprosthesis may also be a problem.

Joint replacements are rarely a onetime event. Over time,revision surgery is typically necessary to repair or replace wornparts of the prosthesis. Depending on the type of prosthesis andthe level of a person’s activity, the time before subsequentsurgery is required may be 10 to 20 years. Ongoing improvementsin methods and materials may eventually extend this period.

Joint Replacement

aging • arthritis • calcium • elbow • fractures and

dislocations • hip • joint disorders • joints • knee • leg

• orthopedics • pain • shoulder • skeletal system

SEE ALSO


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elbow • hip • joint disorders • joint replacement • knee •shoulder • skeletal system • slipped disk • sports injuries

• sprains and strains

SEE ALSO

The body contains more than 200 bones, which are linked byjoints. Some joints are fixed: the bones of the skull, for instance,are bound together by fibrous tissue and cannot move. Otherjoints are lined with a tough elastic tissue called cartilage andallow great movement and flexibility. To avoid friction, movablejoints are lubricated, or kept moist, by fluid from the synovialmembrane, which surrounds the joints.

There are various kinds of movable joints. The joints of thefingers, elbows, and knees are known as hinge joints. They canmove backward and forward. Pivot joints, such as those at thetop of the neck, allow rotary movements, such as turning thehead. Gliding joints, such as those of the spine, wrists, and feet,allow a sliding movement. Ball-and-socket joints, such as those ofthe hip and shoulder, enable the bones to move in all directions.

The knee joint is one of the more complicated joint structures(more than it would first appear), and it is one of the joints mostcommonly injured by athletes.

The knee jointWhen a person extends his or her knee beyond the straightposition, it locks. This locking is brought about by a very slightbut important twisting movement of the large bone (the tibia) inthe lower part of the leg. There are two pieces of cartilage, calledsemilunar cartilages, that pad between the cartilage linings ofthe femur (thighbone). One piece of cartilage wedges the outsideof the joint, and the other wedges the inside of the joint.

The outer edge of each semilunar cartilage is attached to two extremely strong ligaments, one running down the outsideof the leg and one running down the inside. These ligamentsform the lateral and medial colateral ligaments of the knee, withthe cartilage forming a sandwich between them. Any twistingmovement of the knee that pulls the ligaments can tear thecartilage. A torn cartilage causes severe pain and sometimes an inability to bend the knee.

The knee also has two ligaments, called the anterior andposterior cruciate ligaments, in the center of the joint for addedstability. One ligament crosses from front to back and the othercrosses from back to front. These ligaments are also vulnerable to tearing, particularly if the knee is dislocated.

Q & AIs it true that muscles canrestrict a joint’s movementagainst the person’s will?

Yes. Limitation of jointmovement usually results whenthe surrounding muscles go intospasm because of pain. This is a protective mechanism to stop the joint from becomingdislocated and to minimize the effects of any injury.

My brother can crack his fingerjoints like gunfire, driving mecompletely crazy. Besides beingannoying, isn’t this bad for hisfingers?

No damage occurs from crackingthe finger joints. The noise iscaused by a slipping of thelateral tendons that hold thejoints in place around the boneends. The tendons slip back intoposition after a little time.

Are there really some joints thatdon’t move at all?

Yes. The bony plates that makeup the skull are fastened tightlytogether by fixed joints calledsutures. These joints are movablein a newborn baby but quicklyknit together.

Joints


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Junk food is food that contains many nutritionally undesirableingredients, such as saturated fats and refined sugar, andrelatively little fiber or vitamins. Junk food is often easily availableor quick to prepare. Fast food, bought for takeout meals, is oftencalled junk food. It includes burgers, french fries, hot dogs, pizzas,fried chicken, and carbonated drinks.

Preserving agents, as well as artificial flavoring and coloring,are also added to some junk foods. A 10-ounce (300-ml) milkshake, for example, is often made with only 5 ounces (150 ml) ofmilk, topped with air, texturizer, coloring, and artificial flavoring.

A half-pound (200-g) hamburgercontains almost two-thirds of thebody’s daily fat needs. A large can of soda may have as much as 12teaspoons of added sugar.

Nutritionists say that people whorely on a regular diet of junk food areendangering their health. Too manycalories in the form of fat canincrease weight and can lead toheart problems and some forms ofcancer. The refined sugar in softdrinks is also high in calories. Toomany of these drinks can result intooth decay, weight gain, and anumber of diseases. Food and drinkadditives can cause headaches anddizziness. Many food additives seemto be linked with hyperactivity inyoung children, although this linkhas not been proved.

Most young people enjoy junkfood, and a little does no harm.However, if eaten regularly in place of healthy, fresh food, it isdetrimental to health. If someoneeats a balanced diet most of thetime, the occasional junk food mealwill have no lasting ill effects.

This little girl is eating cotton candy.Cotton candy tastes good but contains no vitamins—just the empty calories ofsugar. Eating too much junk food cantake away the appetite for healthier food.

calories • carbohydrates • diet • fats • food additives •food and nutrition • health foods • nutritional

diseases • obesity • sugars • weight control

SEE ALSO

Junk Food


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The knee is the largest joint in the human body. It is strongenough to hold the body upright and enables the lower leg to move, allowing humans to walk and run.

The knee lies between the thighbone (femur) and shin bone(tibia). It is designed like a hinge to allow forward and backwardmovement. The rounded end of the femur rests in the saucer-shaped top of the tibia. A smooth substance called cartilagecoats the ends of both these bones to help prevent friction.Further protection against damage is provided by pads ofcartilage on either side of the knee joint. A small triangular bone, called the kneecap or patella, lies embedded in the tendon in front of the knee.

Special fluid, called synovial fluid, is contained in a capsulesurrounding the whole joint. This lubricates (moistens) the bonesto prevent friction. Strong ligaments hold the knee joint in place.The thigh muscles control the knee’s movement; those at thefront straighten the knee, and those at the rear pull it back.

The knee is highly susceptible to injuries, especially in peoplewho take part in sports. Knee injuries include strains, torncartilage, and a dislocated kneecap.

Q & ARecently, I injured my knee whileplaying a game of football. Inaddition to the pain, which Iexpected, the knee swelled andbecame very stiff. What wouldhave caused that?

The inflammatory response to injury involves a largeoutpouring of fluid into thetissues, resulting in a swollenjoint and stiffness. A doctor maydecide to drain some of the fluidto relieve the condition.

Sometimes, my mother’s kneewon’t straighten. She’s been told that she has a “loose body”in the joint. What does thismean, and can anything be done to fix it?

Any solid material in a joint canlimit its range of movement. Inthe case of the knee, the loosebody can be a bit of cartilage or a chip of bone that may havebroken free. Diagnosis is madeby X-ray examination andarthroscopy. If necessary, loosebodies can usually be removedduring arthroscopy.

Knee

This side view of the knee shows theinternal structure of the joint in detail,including the soft tissues.

femur(thighbone)

muscle

tibia

muscle

tendon

bursa

patella (kneecap)

ligament

cartilage pad

cartilage on bone ends

fractures and dislocations • joint disorders • joint

replacement • joints • ligaments • muscle • skeletal

system • sports injuries • sprains and strains

SEE ALSO


126

The legs enable people to stand, walk, run, and jump. The femur,or thighbone, is the largest and strongest bone in the body. At itstop end, the femur fits comfortably into the hip bone to form aball-and-socket joint that allows the leg to move in all directions.At its lower end, the femur meets the lower leg bones to formthe knee joint. This is a hinge joint that allows the lower leg toswing back and forth. There are two long bones in the lower leg.These are the tibia, or shinbone, which is the heavier of the two, and the narrower fibula. The tibia and the fibula are joinedtogether by ligaments. At the foot, these two bones are joined to the ankle, which is a flexible joint like the wrist.

Soft tissueThe soft tissue of the leg consists of muscle interlaced withnerves and blood vessels. Thigh muscles work in groups withthose of the hip to allow the legs to bend and straighten duringmovement. The thigh muscles also give stability, holding thebody balanced upright when a person is standing. Muscles in thecalf, attached to the knee and ankle joints by strong tendons, alsohelp steady the legs when people stand. These lower leg musclesalso control movement of the feet.

The sciatic nerve that runs down the outside of each leg is the largest nerve in the body. It supplies nerve impulses from thespinal cord to the hip, some thigh muscles, and the muscles ofthe lower leg.

Blood supplyBlood is supplied to the legs by the femoral artery and returns tothe heart through two sets of veins, one set deep inside the leg,the other nearer the surface. The walls of the veins in the leg arethinner than artery walls. Blood has to travel upward toward theheart, so the journey puts considerable pressure on the veins.They are equipped with one-way valves to prevent the bloodfrom flowing backward.

Leg disordersAmong the most common leg disorders is arthritis of the knee orhip, which usually occurs because of wear and tear on the joint.Broken leg bones and damage to the soft tissues of the knee andhip are common in people who take part in vigorous sports.

With age the valves in the leg veins can become damaged,leading to varicose veins. In this condition, the blood flowsbackward in the veins, causing swelling and tenderness. Otherleg problems include ankle injuries, sciatica (inflammation of the sciatic nerve), and artery disorders.

Q & AMy brother has been told that hewill not be able to play soccer fora while because of damage tohis Achilles tendon. What is this?

The Achilles tendon is attachedto the heel and is the linkbetween the foot and thepowerful calf muscles at theback of the leg. These musclesprovide the power for walkingand running; when theycontract, they pull on the tendonand the heel is raised. Thistendon is extremely strong, butoccasionally it gets torn. Surgeryis the only means of repair, and a fairly long convalescence isusually needed.

A car accident has left me withone leg shorter than the other.Can the short leg be corrected by a bone graft?

It might be possible. In a bonegraft, pieces of bone are takenfrom elsewhere in the person’sbody, or from a donor. The graftedbone is used as a supportingstructure around which newbone can develop. Usually it isnot possible to make up morethan 2 inches (5 cm) in length bybone grafting; a longer section ofgrafted bone would be too weak.

Leg


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Leg

The leg bones are the longest andheaviest in the body. The muscles of theleg are also powerful. Those of the thighact with the hip to give stability andbalance. The calf muscles are used inwalking, to steady the legs whenstanding, and to control foot movement.

femur

thigh muscle(quadricepsfemoris)

calf muscle(gastrocnemius)

patella(kneecap)

fibula

tibia

arthritis • circulatory system • cramps • feet • fractures

and dislocations • hip • joints • knee • ligaments •muscle • muscle diseases and disorders • sciatica •skeletal system

SEE ALSO


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The term lethargy, implying a state of drowsiness, is derived fromthe Greek word lethargos, meaning “forgetful.” The term is nowgenerally used to mean indifference to events, a general lack ofinclination to undertake any activity, or an abnormal lack ofenergy. In the opinion of many parents, lethargy is a frequentfeature of teenage life, and it is true that young people cansometimes appear to be dull, apathetic, listless, and sluggish.

Social causes of lethargyIn a few cases, lethargy is a symptom of an organic orpsychological disorder, but the great majority of cases are theresult of social factors over which young people may feel theyhave little or no control. However, this is not necessarily the case.

Lethargy and apathy are often seen as separate conditions.However, although these words are usually defined to suggestthat lethargy is a physical state and apathy is a mental state, the conditions are often inseparable. The relationship betweenthe mind and the body is so interwoven that it is virtuallyimpossible for something to happen to one without affectingthe other. One of the main causes of lethargy, when it occurs asan abnormal lack of energy or motivation, is apathy—an absenceof interest or enthusiasm. A lively relish for life is one of the mostvaluable qualities humans can have, and, for many young people,severe lethargy may be due to lack of interest or participation inevents or ideas.

Interest, motivation, and creativity are also closely linked. Aperson who has become intensely interested in a topic, whateverit may be, will want to become engaged in it and will want to do something with it. Not everyone has the talent or inclinationto paint pictures, compose music, create computer programs, or write the great American novel. However, those who havedeveloped an interest in such activities find that, once thecreative impulse is fully aroused, lethargy disappears.

The physical passivity of lethargy also affects the mindadversely, because everything that happens to the body affectsthe mind. Those who are inactive are likely to develop an inactivemind. Research has shown that most people who engage instrenuous physical activity, such as sports or athletics, have high morale and an optimistic mental outlook.

Medical causes of lethargyLethargy and apathy are characteristic of many serious diseases,especially kidney failure, blood poisoning (septicemia), brainabscess, AIDS, typhoid fever, typhus, hypothermia, exhaustion,and heavy worm infestation. However, some medical causes of

Q & AI’ve put on weight and feeldrowsy all the time andcompletely lacking in energy.Could this be caused by aproblem with my glands?

It is unlikely. In rare cases,however, lethargy can be asymptom of endocrine systemdisorders such as myxedema (a failure of the thyroid gland to produce enough thyroidhormone). In such cases, lethargyis accompanied by weight gain,and the menstrual cycle is oftendisturbed. When lethargy is dueto a disturbance of the hormoneglands, there are usually othersymptoms that point to this as a cause. Check with your doctor.

I’ve heard that I should expect to grow more lethargic as I growolder. Is that true?

No. You may find that yourphysical capacities grow morelimited as a result of the agingprocess, but you should notsuffer from lethargy. Maintainingenergy is a question of havingplenty to do and keeping yourbody in good shape by exercising.You should also keep your brainalert, as lethargy can be theresult of boredom.

Lethargy


129

lethargy are less apparent and can affect young people. Forexample, clinical depression is an important cause of lethargy. It should be distinguished from the normal depressed mentalstate that accompanies physical lethargy from social causes.Clinical (pathological) depression is a serious and dangerousstate featuring sadness out of proportion to any external cause,self-reproach, loss of self-esteem, and, often, suicidal tendencies.It requires urgent medical attention. The same applies toschizophrenia, a mental illness that usually starts in the teenageyears. If lethargy or apathy is associated with evidence ofdelusions (irrational beliefs or ideas) and hallucinations, whichoccur when a person experiences a sensation that has nophysical cause, such as hearing voices or seeing nonexistententities, schizophrenia may be suspected.

Sometimes, lethargy is caused by an underactive thyroid gland.The thyroid gland produces hormones that act on almost everycell in the body, prompting it to activity. A severe lack of thyroidhormone produces marked slowing of mind and body; severelethargy and apathy; dry, scaly, thickened, and coarse skin;cessation of menstruation in women; and a drop in bodytemperature. Treatment with replacement thyroid hormonereverses these symptoms.

Other causes of lethargyPsychological conditions associated with lethargy are post-traumatic stress syndrome, chronic fatigue syndrome, alcohol- or drug-related social problems, anorexia nervosa, and bulimia.Persistent, heavy use of marijuana (cannabis) can induce acondition known as the motivational syndrome, a state of apathy in which there is an unwillingness to do anything and a tendency to drop out of educational and other activities.Lethargy often accompanies loss of ambition and interest.

Many women find that the changes in the hormonal balanceeach month can induce mood changes that lead to lethargy.Lethargy is also common in the early weeks of pregnancy andagain in the first weeks of a baby’s life, when the mother ishaving to cope with hormonal changes and the stress of caringfor a newborn baby. Infectious diseases, viral illnesses, and lack of sleep also lead to feelings of lethargy.

Lethargy

Watching television should not be themain leisure occupation for children. Ameasured amount of viewing mixed withplenty of stimulating activities is a goodway to ward off lethargy.

Playing a game such as baseball is ahealthy way to enjoy fresh air and get exercise, and it is an invigoratingalternative to doing nothing at all.

SEE ALSOaging • anorexia and bulimia • exercise • glands • skin

• sports • tiredness


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Ligaments are strong, straplike bands of connective tissue. Theybind bones together at the joints and, like the hinges of a door,prevent the joints from moving too far. Without ligaments, boneswould be dislocated very easily. Sheets of ligaments hold internalorgans such as the kidneys and spleen in place, and fine strandsof ligaments give support to the breasts. Ligaments are bothtough and yielding. They consist of bundles of fiber made up of a tough, white protein called collagen and smaller amounts of a more elastic protein called elastin. Ligaments suffer damage if they are stretched too far. Injuries include sprains and strains,particularly of the knee, wrist, ankle, and shoulder. Ligamentsmay also tear or become detached from the bone. Treatmentincludes rest, ice therapy, and supportive bandages. Most injuriesheal easily. In severe cases, surgery may be necessary.

Q & AMy father enjoys squash, but hekeeps dislocating his shoulderwhenever he tries to play. Canhis ligaments be strengthened?

Ligaments are not elastic, so it is a question of their beingshortened, not strengthened.Recurrent dislocation can also be due to muscular deficienciesor problems in the joint, so yourfather should see his doctor for a checkup. Stretched ligamentscan shorten, but they need rest; playing squash may beaggravating the problem. Ifnecessary, some ligaments canbe shortened surgically.

My sister has terrible posture.Could this be because herligaments are slack?

Many ligaments becomestretched as a result of long-term poor posture, but this is aneffect, not a cause. Unless thereis a structural abnormality, poorposture is usually due to poorhabits. When people allow theirpostural muscles to weaken, theligaments have to bear the strainand this gradually stretchesthem. Postural reeducation andexercise will help your sister toimprove her posture.

Ligaments

The structure of aligament includeselastin and collagenfibers. The ligamentsof the elbow preventsideways movement.

elastin fibers

collagen fibersbiceps muscle

ligaments

tendon

radius

ulna

humerus

elbow • hip • ice therapy • joint disorders • joints •knee • leg • muscle • shoulder • sports injuries •sprains and strains • tendon

SEE ALSO


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Malnutrition is any form of poor health caused by not eatingenough food or by eating the wrong kind of food in the wrongamount. People should eat appropriate quantities of quality food,and it should contain all the vitamins, proteins, carbohydrates,fats, and minerals needed to keep the body healthy. In developedcountries, obesity due to a poor diet with high levels of fat andlots of junk food is a type of malnutrition. Elderly people andhospital patients may also suffer from malnutrition, becausethey may not be able to look after themselves properly and maybe too weak or ill to eat properly.

The most obvious malnutrition, however, is the starvation thatoccurs in some countries in the developing world. Their foodgenerally lacks protein, and there may be far less food thanpeople need. In many countries, half the children die before theyreach the age of five. Conditions are made worse by famine,drought, and war. These countries cannot afford to import food.Moreover, it often proves difficult to distribute donated food tothose who most need it. As a result, people suffer from varyingdegrees of starvation and do not get enough nutritious food to maintain health.

Lack of proteinThe most common cause of malnutrition is lack of protein, whichoccurs in some African countries. Kwashiorkor and marasmus aretwo diseases that afflict young children. Weight loss; retardedgrowth; wasted muscles; dry, inelastic, cold skin; and sparse hairare typical symptoms of these diseases. Antibodies are made ofproteins, and a severe shortage of protein therefore results in afailure to make antibodies. That causes severe immune deficiencyand probable death from infection. If treated early with a dietbased on milk and high-calorie food supplements, protein-deficiency diseases can be cured.

Voluntary starvationFew people endure starvation out of choice. Some, however, fast for dietary or religious reasons, and such fasting can causesevere malnutrition if practiced regularly. Anorexia nervosa is a starvation disease that is common in young girls who begin dieting to lose weight. Soon, losing weight becomes acompulsion, and the sufferer may take appetite suppressants and laxatives. If untreated, anorexia nervosa can result in death.

The elderly As people grow older they generally become more frail andexperience loss of strength and balance. It is therefore

Q & AMy great-grandmother says she lost all her teeth because of malnutrition during WorldWar II (1939–1945) in England. Is this likely?

No. It seems more probable thatshe just had poor teeth prone todecay. As a result of governmentaction, the standard of nutritionin Britain during the war wasbetter than before. There was nojunk food; there were plenty ofvegetables; free milk, cod liver oil,and orange juice were providedfor children; and common foods,such as margarine, weresupplemented with vitamins.

Could an old man who cannotafford meat have malnutrition?

If he eats other protein, such asnuts and cheese, his diet shouldbe adequate. However, the elderlycan easily become malnourished,especially in the winter.

Are vitamin supplements reallynecessary?

If people eat a balanced dietcontaining all the proteins, fats,carbohydrates, vitamins, andminerals they need, there shouldbe no need for supplements.

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particularly important that the elderly eat sufficient amounts of suitable food, including protein, selected vitamins, and dietarysupplements to help overcome these effects of aging.

Studies have shown that a lack of specific nutrients—including protein; vitamins A, D, and C; and the B vitamin folate—increases the risk of becoming frail. As people age, their ability to absorb nutrients from food also decreases. In addition, manyelderly people may have a fixed income, which affects the qualityand quantity of the food eaten. However, frailty may be easilyprevented and even reversed: meat, beans, and nuts are excellentsources of protein and folate, and fruits and vegetables are goodsources of vitamins A, C, and D.

TreatmentMalnutrition is treated, whenever possible, by gradually givingthe patient a full, balanced diet (a sudden change in eatingpatterns could be too much for a malnourished body to copewith). Sometimes, vitamin and mineral supplements may benecessary for a while, and any medical problems need to betreated. Normally, however, there is no need to take extravitamins or minerals, and they can even be harmful. Eatingproperly should provide all the nourishment needed.

Malnutrition

When a child suffers from malnutrition,the limbs may become wasted while the belly is distended. The child becomesmore and more lethargic, and the facebecomes pinched and gray, with sunkeneyes. This condition is known asmarasmus. The most common cause isstarvation, although marasmus can alsobe a symptom of certain illnesses thatstop the child from taking in nourishmentfrom his or her food.

anorexia and bulimia • diet • food and nutrition •junk food • milk • minerals • nutritional diseases •obesity • protein • vitamins

SEE ALSO


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Massage is a treatment often used for dancers, athletes such as football players, and anyone else who engages in strenuousactivity. It is used to help relieve the stiffness that is associatedwith hard exercise and stops the muscles from becoming tootaut. Massage also promotes relaxation and reduces tension and stress in the body.

There are different types of massage designed to soothe andstimulate the body’s tissues, muscles, and ligaments. Professionalmasseurs and masseuses are trained in the techniques to use ondifferent parts of the body and for different conditions.

Massage works by stimulating the circulation of the blood andthe functioning of the nervous system. During exercise, wasteproducts are released into the muscles. They often cause stiffnessafter exercise. It can take several days before waste products areeliminated from the body. Massage speeds up this process bystimulating the lymphatic system and blood circulation. Thesoothing movements also appear to help lower blood pressure.

A massage can relieve headaches and release muscle tension,promoting relaxation and calm. Many people with stressful jobshave a regular massage, because it promotes mental andphysical well-being in a natural, drug-free way.

Q & AIs a massage carried out forcosmetic purposes the same as a massage used in medicine?

If massage is used to helpsomeone lose weight, it may be very similar to massage formedical purposes. However,facial massage, which is helpfulfor wrinkles, skin tone, andtension, is very light. The facialmuscles are thin, and the richsupply of blood and lymphvessels to this area will respondbetter to light stroking motionsthan to pressure, which would be painful.

Are mechanical massagers good?

Electrical vibration massagerscan be helpful, especially for self-massage. The vibration canaccomplish many of the sameeffects as manual massage andis useful for breaking up depositsof fat and improving the bloodcirculation. The best suchmassagers, although expensive,are the ones that strap onto the back of the hand, allowingthe sensitivity and contact of the hands to direct themovement. However, anelectrical massager should never be used on bony areas.

Massage

Almost any part of the body can be massaged to induce a feeling of well-being. A number of different movements are used in massage. Theyinclude gentle pressure, kneading with the knuckles and the palms of the hands, rolling muscles between the hands, applying friction with the thumbs, and gentle twisting and pulling movements.

blood pressure • circulatory system • exercise •ligaments • muscle • nervous system • physical fitness

• physical therapy • rest and relaxation

SEE ALSO


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Milk is an extremely valuable food. It contains carbohydrates, fats,and protein. It is also rich in vitamin A, vitamin D, calcium, andphosphorus. An 8-ounce (227-g) glass of milk provides about one-third of the daily requirement of calcium. Calcium helps buildand maintain strong bones and teeth. This mineral also plays animportant role in nerve function, muscle contraction, and bloodclotting. The protein in milk contains all of the essential aminoacids in the proportions that the body requires for good health.

Most children and adults drink cow’s milk, although goat’smilk and buffalo milk are drunk in some parts of the world. Ababy drinks human milk from its mother’s breasts; human milkprovides all the nourishment the baby needs in the first fewweeks or months of life. Breast milk contains antibodies that helpprotect the baby from infections. Milk preparations for bottle-fedbabies contain the same nutrients but no antibodies.

Although cow’s milk is an important source of protein andcalcium, it is not a complete food for growing children andadults. They need to add other proteins, vitamins, fiber, andcarbohydrates to their diets. Whole milk also contains a lot of fat(cream), which is not good for health. Nutritionists now believethat it is better to drink low-fat or skim milk, from which most of the cream has been removed.

Q & A

Milk

Q & AWhy does my doctor suggest I drink low-fat milk?

Dairy products, including milk,can be high in saturated fat,which can raise blood cholesterollevels and increase your risk ofheart disease. By drinking low-fat milk, you will reduce your risk of these health problems.

My grandmother insists that Ishould drink a lot of milk. Why?What are the benefits?

Milk contains a large amount ofcalcium, a mineral that yourbody needs to build strongbones and teeth. Duringadolescence, bones grow rapidly,so a teenager in particular needsto make sure that his or her dietincludes enough calcium toguarantee the growth of strongbones. A teenager needs about0.05 ounce (1.3 g) of calcium perday. If a person does not getenough calcium in his or herdiet, the body will take calciumfrom the bones for use in otherparts of the body.

Milk preparations for babies have amountsof fat, carbohydrate, and protein similarto those in human milk. Cow’s milk,whether whole or skim, does not.

calcium • carbohydrates • diet • fats • food and

nutrition • growth • minerals • nutritional diseases

• protein • sugars • vitamins

SEE ALSO

human milk cow’s milk skim milk

dried milk for babies

(reconstituted)

water carbohydrate fat protein


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Minerals such as iron, copper, and zinc are present in the body inminute quantities and are vital for health. These minerals (andmany others) are present in the soil, where they are extracted byplants. Humans obtain the minerals from fruits and vegetablesor from meat and dairy products (derived from animals that feedon plants). Minerals are essential for maintaining mental andphysical health. In the human body, minerals perform a widerange of functions, but a healthy, balanced diet will probablyprovide all the necessary minerals. A lack of iron is one of themost common mineral deficiencies, particularly in developingcountries. Older people sometimes develop a zinc deficiency.Extra minerals should not be taken except when prescribed by a doctor. All minerals can be poisonous if they are taken in excess; iron tablets, for example, can cause serious poisoningin young children.

Minerals

anemia • diet • food and nutrition • iron • salt

SEE ALSO

MINERALS AND THEIR USES IN THE BODYMineral Role Source

Calcium

Chromium

Copper

Fluoride (fluorine)

Iodine

Iron

Magnesium

Manganese

Phosphorus(phosphate)

Potassium

Sodium chloride (common salt)

Zinc

Essential in the structure and working of bones and muscles; important in nerve functioning

Essential for the handling of sugar

Needed for the absorption of iron

Helps protect the teeth against decay

Required for thyroid activity

Required to make hemoglobin and prevent anemia

Important for many body processes; enables thecells to use oxygen

Needed for the control of fats in the body and forthe cells to use oxygen

Basic energy store in body cells; also works withcalcium in bones and muscles

Acts with sodium to control all electrical activity in the body; required by all tissues

Essential component of all organisms; present in all tissues; maintains balance of body fluids

Required for many organisms; present in all tissues;maintains balance of body fluids

Dairy produce, eggs, vegetables

Fats, meat, vegetable oils

Seafood, liver, nuts, cereals

Water

Seafood, vegetables; commonly added to table salt

Meat, egg yolks, green vegetables, cereals

Green vegetables, nuts, cereals

Green vegetables, cereals

Meat, dairy products, fish, legumes, cereals

Fresh fruits and vegetables

All foods; added during cooking

Seafood, meat, nuts


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Motor neuron disease (amyotrophic lateral sclerosis) is oftencalled Lou Gehrig’s disease after the U.S. baseball player LouGehrig (1903–1941), who died from it. The cause of this form of motor neuron disease is usually unknown, but in a smallminority of people there is a genetic cause. The term motorneuron disease, however, covers several similar conditions, of which amyotrophic lateral sclerosis is the most serious.

There are two groups of motor neurons or nerves: the uppermotor neurons and the lower motor neurons. The upper motorneurons run downward from the surface of the brain, throughthe brain and the brain stem and down the spinal cord to end in a series of junctions positioned at the front of the cord from topto bottom. The lower motor neurons emerge from these junctionsto run to and activate the muscles. Motor neuron disease mayaffect either the upper or the lower neurons, or both.

Amyotrophic lateral sclerosis is a combined upper and lowermotor neuron disease. It is more common in men and seldomappears before the age of 50. The motor neurons degenerate untiltheir function is destroyed. When the upper part of the spine isinvolved, there is difficulty in swallowing and speaking, withweakness of the tongue, throat, and voice box. Food may enter the lungs and cause infection, the vocal cords are paralyzed, andthe person cannot cough. The muscles of respiration graduallyweaken so that unassisted breathing becomes impossible.

The pure lower motor neuron types of the disease are muchless severe than amyotrophic lateral sclerosis. They includeconditions formerly known as spinal muscular atrophy andprogressive muscular atrophy, and they vary in terms of the ageof onset. They usually start with wasting and weakness of themuscles of one limb, affecting the hand or foot and progressinguntil the affected limb becomes useless.

Amyotrophic lateral sclerosis is usually fatal. Death oftenresults, within two years, from an inability to breathe, choking, or pneumonia owing to the inhalation of food. Death may alsobe due to malnutrition, because of difficulties swallowing.

The outlook in cases of lower motor neuron disease varieswith the different forms. The recessive genetic adult form startsat any age from 15 to 60 but usually begins in the forties. Limbweakness and serious difficulty with walking seldom occur untilthe sixties or seventies.

Q & AWhat exactly is a motor neuron?

A neuron is a nerve cell. It has a small, spiky body and a longnerve fiber called an axon.Sensory neurons carry nerveinformation to the brain, andmotor neurons carry activatingsignals from the brain to themuscles and glands.

Are the sensory nerves affectedin motor neuron disease?

No; only the motor nerves areaffected. There is no reduction in sensation, and there is nodisturbance of mental functioning.

Motor NeuronDisease

SEE ALSOmuscle • muscle diseases and disorders • nervous

system • physical therapy • spinal cord

The distinguished British physicistStephen Hawking (b. 1942) has sufferedfrom amyotrophic lateral sclerosis fornearly 40 years. He still writes books andgives lectures with the help of a speechsynthesizer and computer.


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All the movements of the body, from the simple twitch of aneyebrow to performing a high jump, are made possible by themuscles. There are three different kinds of muscles: voluntary,involuntary, and cardiac.

Voluntary muscles are under the conscious control of thebrain. They are the muscles that are used when a person decidesto carry out an action, such as raising an arm, turning the page of a book, smiling, or frowning. This type of muscle is also calledstriated (striped) muscle, because it looks striped under amicroscope. Voluntary muscles are attached to the bones byligaments and work in pairs to move the bones. Signals from the brain are carried to the muscles by nerves. When a personwants to raise an arm, for example, chemicals are released that make one muscle contract and pull up the arm. The other muscle of the pair relaxes. Voluntary muscles are oftensubject to injury, but they can self-repair. Sometimes, if onemuscle has been damaged, another muscle will grow larger to compensate for the weakened muscle.

Involuntary muscles control all the things that the body doesautomatically and unconsciously, such as the working of thedigestive system and the bladder. They are also called smooth

muscles, because theyappear unstriped undera microscope. Theycontract slowly andrhythmically. Thesemuscles may bestimulated by nerves, but some of thechemicals in the body,called hormones, can also control them.

Cardiac musclesmake up the main bulkof the heart. Under a

Q & AMy brother tore a leg muscleplaying football, and he’sextremely worried aboutwhether or not he will still be able to play. Will this muscle injury trouble him in the future?

The best way to avoid troublelater on is to gradually build up strength in the injured leg,exercising and training carefullyfor the first two to three weeksafter injury until he can dothings without pain in the leg muscle. The tendency ofrecurrent injury to the samemuscle is much greater if people rush back to being fully active.

What happens physically to a muscle as it is built up andstrengthened?

Adults do not increase thenumber of fibers in a muscle as they train it; the muscle grows bigger and strongerthrough an increase in the size of each individual musclefiber. Whether children can make more muscle fibers byexercise or whether the number of fibers is set bygenetic makeup is unclear.

Muscle

A basketball player useshundreds of voluntarymuscles, unconscious ofthe hard work being doneby his involuntary musclesand heart muscle. Goodmuscle tone and strengthare achieved throughregular training.


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Muscle

SEE ALSObody systems • heart • muscle diseases and disorders •reflexes • sports injuries • sprains and strains

These diagrams show front and backviews of some of the main voluntarymuscles that are located throughout the body.

microscope, they look similar to voluntary muscles. They arecontrolled by a regulating device in the heart itself, and there is no conscious control over this kind of muscle.

occipitalisfrontalisorbicularis oculi

orbicularis oris

sternomastoid

pectoralis major

biceps

external oblique

rectusabdominis

flexors ofwrist andfingers

sartorius

quadricepsfemoris

infraspinatus

teres major trapezius

deltoid

triceps

latissimusdorsi

flexors of ankleand foot

extensorsof wristand fingers

gluteus maximus

hamstringsextensorretinaculum

Achillestendon


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Q & AI strained my thigh muscle last week. The doctor now says I have fibrositis. How did thisproblem happen?

The strain that affected themuscle has caused inflammationwithin the muscle, which can be termed fibrositis. Moreaccurately, it might be calledfibromyositis—myositis implyingthat the inflammation of fibroustissue is in the muscle. In time,the injury should heal and theinflammation will die down.

Muscle Diseasesand Disorders

The most common muscle problems are caused by injuries,which often happen to people who take part in active sports.Pulled, strained, and torn muscles are all the same type of injury.

Muscle injuriesTearing of the muscle fibers and bleeding inside the musclecause pain and swelling. This kind of injury usually heals quickly,particularly in young people. Treatment usually consists ofresting the muscle as much as possible to give it time to knittogether and bandaging it for support. When the pain andswelling have gone down, the muscle can gradually be exercisedback into use. If any injury remains swollen and painful for morethan a few days, a doctor should be consulted.

Sometimes, the whole muscle is torn, or ruptured. Thiscondition is extremely painful, and the muscle will need to bestitched together again. Occasionally, a torn muscle causesbleeding in the muscle and the formation of a blood clot, whichis removed surgically.

Muscle cramps and myositisA cramp is the painful tightening of a muscle or group ofmuscles. It occurs most commonly in the leg muscles, particularlyin the calf. A cramp can come on suddenly, sometimes when aperson is asleep. The muscle fibers contract into a hard knotduring the spasm, which can last from a few seconds up to a

couple of minutes. A cramp can becaused by poor circulation and byexposure to cold. Heavy sweating due to vigorous exercise in a hot climate can deplete the body of salt, causing a cramp. Young people and othersengaging in sports should avoid eatingjust before physical exertion, because the blood is concentrated around theintestines and away from the musclesduring digestion, so a cramp may result. Swimmers are particularly at risk. An attack of cramp can be eased by massaging the affected muscle.Flexing the foot upward or manuallylifting the toes helps to relieve leg and foot cramp.

Inflammation of the muscle sheathsis known as myositis. It can be caused by cold, by excess exercise, or by an

A cramp in the leg can berelieved by flexing the footupward. Persistent crampingis often cured by pacingaround the room for a while.


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infection. Rubbing the area with liniment and taking mildpainkillers can ease the pain.

Causes of diseases and disordersDiseases affecting the muscles are relatively rare. Most muscleweaknesses are caused indirectly: for example, by a problemoccurring in the nervous system, which controls the movementof the muscles. Lou Gehrig’s disease is this type of disorder ormotor neuron disease. Occasionally, a hormonal condition or a lack of vitamin D can result in a weakening of the muscles.Other serious muscle disorders, such as muscular dystrophy, are inherited.

Muscle Diseases and Disorders

A muscle can be pulled, strained, or overstretched in an accident orduring exercise. The main symptomis pain. The type of injury varies. Forexample, dropping a heavy load cancause a sudden, sharp movement or moment of acute tension in aparticular muscle. Attempting to lift something that is too heavy, or lifting awkwardly or incorrectly,can also cause a pulled muscle. Apowerful movement that twists apart of the body into an unnaturalposition, as often occurs inbasketball, may also stretchmuscles beyond their natural limit.

MUSCLE DISORDERS

Disorder Causes Symptoms Treatments

Pulls, tears, strains, and sprains

Cramp

Polymyalgiarheumatica

Myositis

Muscular dystrophy

Hypokalemic paralysis

Hyperkalemic paralysis

Tearing of the muscle fibers,followed by bleeding in andswelling of the affected muscle

Muscle goes into spasm;dehydration may be a cause

Inflammation of the bloodvessels supplying blood to the muscles

Painful inflammation of themuscles, often with associatedconditions; can be caused byinfection

Inherited abnormalities in the working of muscle cells

Low level of potassium in blood

High level of potassium inblood

Pain, which may become worseduring the first few days afteroriginal injury; limitedmovement

Painful tightening of themuscles, often in the calf

Pain, often around the neck andshoulders, and ill-health; affectsonly the elderly

Pain and weakness; blood testsmay show that muscle tissue is being broken down

Progressive weakness of musclesaffecting different areasaccording to the form ofmuscular dystrophy

Periodic attacks of paralysis

Periodic attacks of paralysis

Cold (ice packs, water) andpressure with bandages helpimmediately; later, gentlemuscle movement; heattreatment may help

Quinine may help; salt andwater replacement are vitalwhen dehydration is the cause

Anti-inflammatory drugs

Treatment depends on thecause; rest alone will improvemany types, but steroid tabletsmay help

None, but splints and other aidscan be of considerable value

Requires expert medicalattention

Requires expert medicalattention

PULLED MUSCLES

analgesics • cramps • exercise • motor neuron disease

• muscle • nervous system • pain • sports injuries •sprains and strains • vitamins

SEE ALSO


141141

The nervous system is the body’s complex communications andcontrol network. It collects information around the body throughthe senses of sight, hearing, taste, smell, and touch, and then ittells the body what to do in response. The nervous system consistsof millions of interconnected nerve cells called neurons; they pick up information and send signals from one part of thesystem to another. Neurons are easily damaged or destroyed by injury, infection, pressure, chemical disturbance, or lack ofoxygen.

The nervous system consists of the peripheral nervous systemand the central nervous system. The central nervous systemconsists of the brain and the spinal cord. Together they receivemessages from the body’s sense organs, analyze them, and then send out signals to the muscles and glands. Thousands of neurons are involved in the brain during this assessment. The peripheral nervous system consists of all the nerve tissueoutside the central nervous system. Nerves branch out from the brain and spinal cord and then divide to supply the body. The peripheral nervous system consists of an outer system (the somatic or body system) and an inner one (the autonomicsystem).

The somatic system collects information from the body’s senseorgans and conveys it to the central nervous system alongsensory nerve fibers. It carries signals from the central nervoussystem to the muscles along motor nerve fibers, which aregathered into a bundle called a nerve. Forty-three pairs of nervesemerge from the central nervous system. Twelve pairs come fromthe brain; the rest of them come from the spinal cord.

The autonomic nervous system controls unconscious functions,such as the heartbeat, the narrowing and widening of bloodvessels, breathing, and gland secretion. Autonomic control becomesextremely active in times of sudden physical danger and modifiesbody function to give the body the best chance of survival.

Each neuron has the same basic structure, but neurons are ofvarious shapes and sizes. Each neuron cell has a number of fine,rootlike fibers, or dendrites, projecting from it. Projecting fromthe cell is a single, long fiber called an axon. At its far end, theaxon either ends in a single tiny knob or divides into a number of branches, ending in a cluster of knobs. Each knob is separatedby a minute gap from a dendrite, from another neuron, or fromthe surface of a muscle cell or a gland cell. Messages are carriedacross these gaps by substances called neurotransmitters. Everyneuron has a thin wall known as the neural membrane, which is vital for the transmission of signals. Many axons have aninsulating covering called myelin.

Q & AA friend said the pain I have in my hands and arms could be caused by a pinched nerve.What is this?

At some point along their length,many nerves have to passthrough a restricted space,especially near joints. Anydisplacement or swelling in this space may squeeze or pinch the nerve, causing pain,muscle weakness, numbness, or a tingling sensation.

Two months ago, my grandfatherhad a foot amputated. I’mextremely confused because he still feels that the foot isthere and even has pain fromthe missing toes. Why does this happen?

Although his foot has beenamputated, the sensory fibersthat used to send messagesfrom the foot to the brain arestill present in the remainingpart of his leg and have theirendings in the stump. If theseendings are stimulated, thefibers send messages via thespinal cord to the brain, which,from past experience, interpretsthe message as having comefrom the foot.

Nervous System


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Nervous System

How the brain, spinal cord, and peripheralnervous system work together is complex.Thousands of messages, determining evensimple reflex actions such as turning thehead, are transmitted and received viapathways out of and into the spinal cord.From the central nervous system (brainand spinal cord), pairs of nerves radiate all over the body, forming the peripheralsystem. This system has two mainsubdivisions: the autonomic system(unconscious control of functions such as breathing) and the somatic system(conscious control).

cerebrum cerebellum

cervical nerves (8 pairs) supplying neck,shoulders, andarms

brain

cranial nerves(12 pairs)

spinal cord

autonomicsystemnerves

somatic systemnerves

spinal nerves

thoracic nerves(12 pairs)supplying trunkand arms

lumbar nerves(5 pairs)supplying legsand lower back

sacral nerves (5 pairs) supplying legsand genitals

coccygeal nerves (1 pair) supplying coccyx

SEE ALSObody systems • motor neuron disease • pain • spinal

column • spinal cord


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A nosebleed is caused by the breaking of a small blood vesselinside the nose. It may be the result of direct violence, injury,sneezing, or picking the nose. Some people have a nosebleedwhen they have an attack of hay fever or have a nasal infection. If the membranes lining the nose become dry and cracked,bleeding may occur. Sometimes, there is no obvious reason for it. Girls who have recently started to menstruate often havenosebleeds with no apparent cause.

A broken nose, one of the most common sports injuries, oftenresults in a nosebleed and requires immediate medical attention.Almost invariably, a broken nose will be out of shape. If it isallowed to heal without being reset by a surgeon, it will lead in most cases to other problems, such as chronic runny nose or sinusitis (inflammation of a sinus).

First aid for a nosebleedThe person with a nosebleed should sit quietly, loosen the clothesaround the neck, and lean his or her head slightly forward (notback) to help prevent any blood from being swallowed. He or sheshould pinch together the nostrils until the bleeding stops, whilebreathing gently through the mouth. If bleeding continues, asmall, clean piece of gauze should be inserted just inside one or both nostrils, which should then be pressed together. It isimportant not to force anything up the nose. When the bleedingstops, it is important that the patient does not keep touching the nose. If bleeding does not stop, a doctor should be consultedor the patient should be taken to a hospital.

Serious nosebleedsSometimes, an artery at the back of the nose is damaged,causing extremely heavy bleeding. That situation needstreatment by a doctor, who will pack the nose. Other nosebleedsalso need attention from a doctor: those caused by a blow, thosethat happen within a week or so of a tonsil or adenoid operation, and those lasting for more than about 20 minutes. Otherwise,home treatment is usually sufficient.

Although nosebleeds can often be alarming, not much blood is lost, even during a heavy nosebleed. Normally, a nosebleedclears up in five to 15 minutes, which is the time it usually takesfor blood to clot.

Q & AI’ve heard that a nosebleed is a sign of pressure on the brain.My brother has had severalnosebleeds recently. Is thisserious?

Nosebleeds are common inchildren, perhaps because theyare so active and thus are likelyto have many minor injuries.Some children are more prone to nosebleeds than others. Afrequent cause is that bloodvessels just inside one or bothnostrils have burst, afterbecoming weakened andenlarged through rubbing andpicking, or because of previousnosebleeds. Pressure on thebrain is not a cause. However,recurrent bleeding can be asymptom of disease, so yourparents should consult yourbrother’s doctor.

My grandmother used to put a cloth soaked in witch hazelacross my nose when it bled. Is this an effective cure?

Although some herbs may haveproperties that help stem theflow of blood, it is more likelythat your grandmother’streatment acted as an effectivecold compress.

Nosebleed

circulatory system • ice therapy • sports injuries

SEE ALSO


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The body can work properly only if it receives the right materials,including certain vitamins and minerals. Without them, peopledevelop diseases such as scurvy and rickets. In the past, althoughit was known how to prevent certain diseases, it was not knownwhat the causes were. Experts are now learning more about thesubstances the body needs. In developed countries, few peoplesuffer from deficiency diseases. However, in some countries inthe developing world where people have an inadequate diet,there is a serious problem.

Sometimes, people do not eat properly because they cannotget enough food. Others do notknow what to eat or do not eatsensibly. Alcoholics often getdeficiency diseases, for example,because they do not eat properlyand do not absorb fats and vitamins.Beriberi (degenerative changes ofthe nerves, digestive system, and the heart) is caused by lack ofvitamin B1 (thiamine). However, most deficiency diseases are easy to cure with a proper diet. The dietmay be supplemented with largedoses of the substance that hasbeen lacking.

A few people have nutritionaldiseases even though they areeating properly, because their bodiesare unable to take in or use certainsubstances properly. For example,some people become anemicbecause their bodies cannot absorbvitamin B12. If people eat sensibly,they should get everything theyneed from their food. Vitamin andmineral supplements should betaken only if a doctor prescribesthem, because too many vitaminscan be harmful.

NutritionalDiseases

anemia • calcium • diet • digestive system • food and

nutrition • iodine • iron • malnutrition • milk •minerals • protein • salt • scurvy • vitamins

SEE ALSO

CONDITIONS CAUSED BY NUTRITIONAL DEFICIENCYVitamin or

mineral deficiency

Diseases and

disorders

Deficiency

corrected by

Vitamin A

Vitamin B1(thiamine)

Vitamin B (niacin)

Vitamin C

Vitamin D

Iron

Sodium

Iodine

Skin diseases, severeconjunctivitis, nightblindness

Beriberi (weakness,swelling), confusion, heart failure

Pellagra (a skin disorder),diarrhea, dementia,dermatitis with skinblistering

Scurvy, slow woundhealing, anemia,hemorrhages from toothsockets and into joints

Disorders of boneformation leading toswelling, softening, andbowing of bones (calledosteomalacia in adultsand rickets in children)

Anemia

Disturbances of bodychemistry

Goiter (swelling ofthyroid gland), cretinism

Dairy products, eggs, liver,oily fish, vegetables(especially carrots)

Bran, cereals, pork, liver

Liver, kidney, yeast, fish,cereals

Fresh fruits and vegetables

Milk, egg yolk, cod liver oil, fortified milk andmargarine, action ofsunlight on skin

Lean meat, liver, spinach,cabbage, legumes, eggs

Salt

Seafood


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If the amount of food people eat exceeds the energy used, theywill become overweight. If a person’s weight is 20 percent ormore above normal for his or her height and age, there will be anaccumulation of body fat and the person will be obese. Obesitycan be prevented by sensible eating and by exercise. It can becured by dieting and then eating carefully. This is not easy, but it is worth doing. Obesity is a serious condition, because itincreases the risk of developing various chronic health problems.

CausesThe amount of food someone’s body uses varies a great dealfrom one person to another, but if a person is gaining weight, he or she is eating more than is needed. The excess food isconverted into fat that is stored under the skin, first in cells in thebuttocks and around the waist, and later in the thighs, shoulders,and arms. Very rarely, a medical problem such as an underactivethyroid gland causes obesity by greatly reducing energyexpenditure. Medical tests will find out if there is any such cause.Bad eating habits are the most common cause of obesity. Often,all the members of a family are obese, because they have similarhabits. Emotional problems can make people overeat for comfort.

Dangers and treatmentsExtra weight puts strain on the joints, particularly the knees, hips,and some of the back joints. It causes wear and tear, which maybecome a painful problem. Someone with a very fat stomachcannot breathe properly, and he or she will have shortness ofbreath and lung problems. Obesity can cause gallstones; mild

diabetes, in turn causingserious complications inthe small blood vessels of the eyes and kidneys;thickening of the arteries,which increases thelikelihood of suffering a stroke or heart attack;and high blood pressure.

Q & AMy friend eats the same amountas I do, is about the same heightas I am, but is of average weight,whereas I am fat. Why is this?

The way in which people’s bodiesuse food varies widely. Peoplewho use their food fueleconomically become obesemore easily than those who useit extravagantly, because theyburn off less energy for the sameamount of work. You may alsofind that you are getting lessexercise than your friend, so thatyou are expending less energy.Finally, you may have acquired anexcess of fat as a child, so thateven if you eat the same as yourfriend, you are still not losingyour excess stored fat.

Is it true that gland trouble cancause obesity?

People are rarely overweightbecause of an underactivethyroid gland or overactiveadrenal glands, and in thesecases, there are other symptoms.

Obesity

This woman has resorted to desperatemeasures to help reduce her weight. Shehas had her teeth wired so that her jawsare clamped together. She can consumeliquids only.

anorexia and bulimia • blood pressure • calories •circulatory system • diabetes • diet • dieting • exercise •food and nutrition • glands • heart • heart attack • hip

• isometric exercises • joint disorders • joints • knee •sports • stroke • weight control

SEE ALSO


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The term orthopedics derives from the Greek root ortho, meaning“straight.” Orthopedics is the surgical specialty that is concernedwith disorders and deformities of the bones, joints, ligaments,muscles, and tendons. The specialty is also concerned with nervesthat are involved in skeletal injuries or in conditions leading tomuscle weakness. Orthepedics covers many disorders involvingthese body systems. Some disorders are present at birth(congenital) and some are acquired later in life. They may beinflammatory and due to infection; degenerative or the result of tumors; or, in many cases, due to injury. An important part of orthopedics is the treatment of the complications of thevarious forms of arthritis.

Fractures and other bone disordersOrthopedic surgeons treat difficult fractures, especially whenrecovery is delayed or complicated by soft-tissue injuries, or whenthe break is adjacent to nerves and blood vessels. Most fracturesheal satisfactorily if the limb is immobilized with a plaster cast or by other means. However, if healing is hindered, orthopedichelp is needed. Some fractures are so fragmented that theycannot be kept in alignment or immobilized by an external cast. Sometimes, there is damage to blood or nerve supplies.Compound fractures (those that involve open wounds) needtreatment by a specialist. In some cases, fractures that have not united need bone grafting. Orthopedic surgery can involvefixing a fracture with screws, plates, or nails inside the bone.

Orthopedists are also concerned with other bone disorders,including bone growth failure, bone softening, bone distortionfrom rickets in children or from osteomalacia in older people,bone tumors, and tuberculosis of the bone. Degenerative bonediseases and congenital defects of the skeleton require careful

Q & AMy brother had an accidentrecently and is in a body cast.Will his skin suffer?

The skin grows even when it iscovered by a plaster cast. Whenthe plaster is finally removed, the skin will look dirty and havethe appearance of sandpaper,because it has continued to growand has shed scales. This is not a long-term problem and shouldimprove within a few weeks.

When a person breaks a bone, is it best to have a bone graft or to have a pin inserted?

It is always better to let thingsheal naturally wheneverpossible. A pin, a plate, oranother piece of metal is used in the join only if the orthopedicsurgeon believes the fracture will not unite firmly without it. A pin holds two bones together;a graft adds bone pieces that are missing. A cast keeps theinjury immobile during thehealing process.

Orthopedics

If a bone is fractured in several places,external pins may be used to immobilizeand fix the bone. The pins are insertedthrough the skin into the bone and areheld in place externally with a metal rod.


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management. One advance in orthopedics is the use of bone-lengthening procedures to treat certain forms of dwarfism. With a growing elderly population, the incidence of osteoporosisin women after menopause is becoming increasingly high.Osteoporosis can make bones so brittle that they break easily.Spinal bone problems in older women are usually due toosteoporosis. Fractures of the neck of the femur are also commonin women with osteoporosis. The blood supply to the head of thebone may be cut off when the femoral neck is fractured. That canlead to the need for an artificial hip replacement, which is one ofthe most common operations performed by orthopedic surgeons.

Joint injuries and foot conditions Joint injuries are common and range from simple sprains, in which some of the ligaments are slightly stretched, to radicaldislocations with extensive soft-tissue damage. Some joints, such as the shoulder joint, are liable to recurrent dislocationsthat require surgery. Other common orthopedic problems arejoint disorders of the knee from twisting injuries or direct force,in which the cartilage of the knee joint is torn and displaced,with locking of the joint. The internal ligaments, which stabilizethe joint, may be stretched or torn. Various surgeries are done on the interior of the knee joint with an arthroscope, a fineinstrument that is passed into the joint through a tiny incisionthat allows illumination and visualization, and the use ofspecially designed surgical instruments. Tears of external knee ligaments may be repaired by open surgery.

The joint between the big toe and the first long bone of thefoot (metatarsal) is commonly distorted by a genetic tendency or by unsuitable shoes to form a bunion, a bony bulge withoverlying soft tissue. In severe cases, the only treatment is tochisel off the bony bulge. Other orthopedic foot conditionsinclude congenital clubfoot (talipes), flatfoot, and hammertoe (in which a toe is fixed in an angular position). Inflammatorydisorders of joints are common and can be hard to treat. Some,such as gout, can be treated medically and do not involveorthopedics. In many cases, however, orthopedic surgery is invaluable in restoring comfort and function by jointreplacement.

Orthopedics

This X-ray shows a spiral comminutedfracture of the tibia and fibula, which are the bones of the lower leg. In this typeof fracture, the bone is broken, splintered,or crushed into a number of pieces andwill require orthopedic treatment.

arthritis • fractures and dislocations • joints • knee •ligaments • muscle • muscle diseases and disorders •shoulder • skeletal system • skin • sprains and strains

SEE ALSO


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Osteopathy is a system of diagnosis and treatment thatrecognizes the role of the muscles and skeletal system in thehealthy functioning of the body. An osteopath is a medicalpractitioner who has graduated from an osteopathic medicalschool and holds a doctorate in osteopathic medicine (DO).

Osteopaths stress the importance of the correct functioning and position of the bones, the muscles, and their connecting tendons and ligaments in general health. They concentrate on musculoskeletal manipulation and take a distinctly holistic(whole-person) approach to consultation, diagnosis, and practice.Osteopathy also focuses on promoting wellness, rather thansimply treating the symptoms of a disease.

Osteopathic treatment includes manipulating the bones,muscles, and joints to relieve pain and discomfort, improvemobility, and restore body control mechanisms. Most people visit osteopaths because they have sports injuries, back pain, or restricted movement in a joint. An osteopath is usually able to treat patients successfully using a combination ofmanipulation, rhythmic stretching, and pressure.

Q & AAre chiropractors and osteopathsthe same?

No. Chiropractors practice onlymusculoskeletal manipulations.Osteopaths may do somemanipulation, but they are fullytrained and qualified physicianswho can prescribe medicines,whereas chiropractors cannot.

SEE ALSOchiropractic • joint disorders • joints • ligaments •muscle • skeletal system • sports injuries • tendon

Osteopathy

Osteopathic treatment begins with athorough examination of the patient. The osteopath then decides what type of manipulative treatment to apply.


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Oxygen is a gas, with no smell, taste, or color. It makes up aboutone-fifth of the air that people and other animals breathe.Oxygen is an important substance on which many forms of lifedepend.

People cannot live for more than a few minutes withoutoxygen, because it is essential for producing energy. The maintask of the lungs, heart, and blood vessels is to carry oxygen fromthe air to every part of the body. The brain, in particular, requiresa large, continuous supply of oxygen. Deprivation of oxygen formore than a few minutes usually produces serious brain damageand is often fatal.

A shortage of oxygen in the body shows up as a bluenessaround the lips and tongue, a condition known as cyanosis.People most likely to suffer from a shortage of oxygen are thosewith lung disease, including chronic bronchitis, acute attacks ofasthma, pneumonia, and emphysema.

Heart complaints that keep the lungs short of blood can causeoxygen starvation, and patients have to be given extra oxygenthrough a mask.

Oxygen therapyOxygen is by far the most vital element for human life andhealth. Failure to get an adequate supply of oxygen to the body’stissues causes a range of diseases in which the intake of oxygento the blood or the supply of blood to the tissues is reduced.Oxygen therapy is often an essential part of medical treatment.

Hyperbaric (high-pressure) oxygen therapy provides a massivesupply of oxygen to thepatient’s tissues. This is necessary in heartsurgery and is helpful intreating carbon monoxidepoisoning, decompressionsickness, and nonhealingwounds. Infections thatfunction only in theabsence of oxygen, such as tetanus and gas gangrene, can also be treated with oxygen.

Q & AMy grandfather is in the hospitaland has to have oxygen. Will he always need this extra supplyof oxygen?

No; he is unlikely to need extraoxygen when he leaves thehospital. The usual reason peopleare given oxygen in the hospitalis that they have an acute heartproblem or an infection in thechest when they already sufferfrom a long-term chest ailment.The extra oxygen helps themwith the immediate difficulty,and it is controlled very carefully.

I often feel tired and lethargic.Am I short of oxygen?

No, probably not. Everybody feelstired sometimes, but oxygenshortage is rarely the cause.Some heart or lung conditionscan make a person breathlesswith exercise. Anemia, however,can cause a person to becometired and listless and involves a low oxygen level. Consult your doctor if you are worried.

Oxygen

Green plants give off oxygen, which isbreathed in by humans and otheranimals; they breathe out carbon dioxide,which is taken in and used by the plants.This is known as the oxygen cycle.

oxygen

carbondioxide

SEE ALSOanemia • asthma • circulatory system • heart • heart

attack • lethargy • respiratory system • tiredness


150

Pain is the body’s alarm system. It acts as a warning whensomething is wrong. Pain should never be ignored; neithershould people keep taking painkillers to blot out pain if they donot know what is causing it. A doctor should be able to find outwhy the pain exists and provide the treatment needed to cure it.

Causes of painPain is caused by something stimulating the tiny nerve ends thatare present in all parts of the body. Sometimes, pain produces aninstant reaction. If a person touches something very hot, thebody will draw back the hand faster than he or she can think.Sensory nerves have taken the message “hot’’ to the spinal cord.The motor nerves have acted immediately to remove the handfrom the danger. At the same time, nerves are taking messagesto the brain, which figures out more slowly what is happening.Internal pains work in the same sort of way.

Types of painsThere are many kinds of pains—from sharp, knifelike pains todull, throbbing aches. Acute pain is usually intense and short-lived. It may be caused by a burn, a cut, or a blow. Sometimes,acute pain is so severe that the blood vessels dilate, the bloodpressure drops, and the person loses consciousness. Chronic pain

Q & AWhy can pain cause a person to faint?

The parts of the brain thatreceive and analyze painfulstimuli have close connectionswith the parts that have overallcontrol of blood circulation, the heartbeat, and the conditionof the peripheral blood vessels.Even a small degree of paincauses some change in aperson’s pulse rate, bloodpressure, or both. If pain issevere, the circulation can beswamped by these influences:the blood vessels dilate and theblood pressure drops so low that unconsciousness results.This process is the same for any severe unpleasant stimulus,although people vary as to whatdegree of pain causes fainting.

Does acupuncture work onlypsychologically to relieve pain?

Psychological factors are veryimportant in any method of pain relief, because of theconsiderable psychologicalcomponent in the appreciationof pain. However, it is likely thatthere is a genuine physiologicalmechanism at work in somemethods of acupuncture.

Pain

Some cultures make a virtue of pain; this man, taking part in a Hindureligious ceremony, has both cheeks pierced by a metal rod. Like somepractitioners of Eastern religions who walk barefoot over red-hot coals, he has a high tolerance of pain. He has trained his mind to ignore painfulreactions by concentrating on other—usually spiritually uplifting—things.


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Touching a hot iron (top) causes a sharppain, followed by a burning sensation.Earache (bottom) may be a dull,persistent pain.

Pain

This diagram shows the pathways bywhich sensations of pain travel to thebrain. Analysis of pain begins in the brain stem and goes either directly or on a more meandering course to the thalamus, which is the brain’s main sensory relay station.

thalamussection through brain

cerebral cortex

midbrainfast conductingpathway of painto the brain

slowerpathway of pain to the brain

message sent to remove hand frompainful stimulus such as hot iron

brain stem

spinal cord

is persistent over a relatively long period of time and is invariablythe sign of some disorder. It is often characterized by a deep, dull,aching pain. There are many different causes of chronic pain.Sometimes, it is easy to sense where a pain is coming from.


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In other cases, pain may seem to come from some general area.To make matters more complicated, pain from some organs ofthe body may seem to be coming from quite another place. Painfrom the heart is felt in the center of the chest and in the leftarm and jaw, for example. This is known as referred pain; itoccurs because sensory nerves running to a particular segmentof the spinal cord may come from widely separated points,and nerve impulses coming from one of these areas may be interpreted as coming from the other.

Phantom limb painWhen an arm or a leg has been amputated, the nerves remain in the stump. If something stimulates their endings, the brainwill register the pain as though it were coming from the missinglimb. It may take some time before the brain comes to termswith the fact that the limb is no longer there.

Sensitivity to painSome people are much more sensitive to pain than others. Whatis a slight hurt to one person may cause genuinely severe pain to another. A person may also feel a pain much more at one time than at another. In the case of sudden, unexpected severeinjury, when pain should be extreme, the injured person may feel little or no pain. In such circumstances, the brain producesmorphinelike substances called endorphins, which are highlyeffective in controlling pain. During a battle, for example, awounded person may hardly notice his or her injury.

Relieving painAnalgesics and other drugs are used to control pain. Narcoticssuch as morphine, codeine, methadone, and meperidine, whichare addictive, are used for only a limited time, such as aftersurgery or a severe injury. There is also a wide range of non-narcotic painkillers. Aspirin and acetaminophen are the mostcommonly used for minor aches and pains, and prescriptionanalgesics such as propoxyphene may be given by a doctor forcertain other types of pain. It is inadvisable to take over-the-counter painkillers for longer than two or three days. If the painpersists, a doctor should be consulted.

Pain

PAIN RELIEF WITHOUT DRUGS

Transcutaneous electrical nervestimulation (TENS) is often used for neck and back pain, phantomlimb pain, and nerve injury andinfection. A tiny portableinstrument delivers low-voltagepulses, stimulating nerves thatblock out the pain. Electrodes areplaced on the skin at trigger points,and the instrument is turned onwhen needed.

Acupuncture is effective for alltypes of pain, because acupunctureneedles stimulate nerves thatsuppress pain.

Biofeedback machines measureautomatic body functions such asmuscle tension and brain waves.After training, a person withmigraine or tension headaches canrecognize the automatic responsesthat trigger pain; the machines areusually equipped with a warningsound signal. The patient is thenable to control the pain byconsciously relaxing the muscles or by dilating the blood vessels.

SEE ALSOacupressure • acupuncture • analgesics • nervous

system • spinal cord


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Paraplegia is damage to the middle or lower area of the spinalcord that can cause paralysis of both legs and sometimes part ofthe trunk. The connection between the brain and the nerves usedfor movement is cut. If the damage to the spinal cord is high inthe neck, the arms and the legs are also paralyzed, a conditionknown as tetraplegia or quadriplegia. Most cases of paraplegiainvolve both legs and the lower part of the trunk.

The most common cause of paraplegia is spinal cord damagefrom a physical force that fractures and dislocates the spine,compressing or severing the spinal cord. Several small strokesaffecting both sides of the brain can also cause paraplegia.

Spinal cord injury can also result from diseases that affect the spinal cord, including myelitis (cord inflammation), multiplesclerosis (MS), poliomyelitis, and blockage by a blood clot in thespinal artery. In children, paraplegia can be caused by congenitalmalformations of the spinal cord or by early brain damageleading to cerebral palsy. Early rickets, with softening anddistortion of the spine, can also cause cord damage and paraplegia.

The degree of damage to the cord determines the degree ofsensation that is lost. In some cases, there is paralysis and loss of sensation in the entire body below the level of the injury. In

addition to the inability to walk,paraplegia often causes problemswith bladder and bowel control.

Much research is now under wayto find ways to rejoin nerves. Already,paraplegia has been cured in smallanimals, and experts are optimistic.In addition, a frame that allows a paraplegic to walk has beendesigned. The frame has leg bracesand splints and is assisted by thearms and by electric motors.Improvements in the design are being made constantly.

Electrical stimulation of theparalyzed leg muscles to make themcontract and allow a paraplegic towalk are also being developed.

Q & AI have recently been confined to a wheelchair. Should I changemy diet?

Yes. You should be eating muchless than before. Because you area lot less active, you will not beable to burn up as many calories;thus you are likely to put onweight, which is not easy to losewhen you are confined to awheelchair.

Paraplegia

Paraplegia does not prevent people fromplaying competitive sports. Esther Vergeerof the Netherlands is seen here playing in the paralympics in Sydney, Australia, in 2000.

SEE ALSO

leg • muscle • nervous system • spinal column • spinal

cord • sports • stroke


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A physical examination is usually a part of a consultation with a physician. Generally, only the area of the body that is affectedwill be examined, but on occasion, the doctor will give thepatient a thorough examination. Children and teenagers shouldhave several physical examinations during their growing period.Many companies insist that their key employees have regularcheckups. Such examinations can detect the onset of diseasebefore any symptoms appear.

A typical physical examination would include palpating(feeling) the abdomen and other parts to discover anytenderness or swelling. The doctor also percusses (taps) the chest and abdomen to detect whether there are areas ofunexpected dullness or resonance. The doctor listens through a stethoscope to sound-producing organs such as the heart and lungs. Other tests may include measuring blood pressure,having a laboratory analyze urine and blood, taking X-rays, and perhaps taking an electrocardiogram.

In 1987, the American Heart Association recommended that, to detect and prevent heart and blood disease, everybody shouldhave regular checkups every five years from the age of 20. Afterpeople reach 65, the checkups should be every two and a halfyears. At age 75, the examinations should be done every year.

Q & AMost of the time, I just don’t feel very good. Should I ask mydoctor to give me a thoroughphysical examination?

If you feel bad for any length oftime, it is important that you goto your doctor to find out what iswrong. Normally, he or she willbe able to assure you that thereis nothing wrong. However, ifthere is any doubt, the doctorwill probably recommend a full physical examination.

Someone told me that all childrenshould have an annual physicalexamination. Is this right?

It is certainly wise for children tohave regular medical and dentalcheckups to make sure that theyare developing normally and thatthere are no signs of disease. It isnot usually necessary, however,for these to be done as often asonce a year. It is desirable thatadolescents have a checkuptwice a year during their time of most rapid growth.

PhysicalExamination

This woman is having her blood pressurechecked. High blood pressure can beextremely dangerous; low blood pressurecan signal inadequate blood flow tovarious parts of the body.

SEE ALSOaging • blood pressure • body systems • cholesterol •growth • physical fitness • puberty


Physical fitness is not simply exercise. It means getting andkeeping the body in a condition that will maintain good health,while developing physical endurance and skill so that life can beenjoyed to the fullest through functioning at the best physicallevel. Physical fitness involves a healthy, balanced diet, which is necessary to fuel the body and its muscles properly.

To achieve physical fitness, people also need to have the rightmental attitude. If they recognize the health benefits of physicalfitness, they must be willing to put in the effort to build upstamina and endurance in the sports, exercise programs, andfitness activities they most enjoy.

Benefits of physical fitnessThe benefits of physical fitness are that a person looks and feels better and the ordinary everyday tasks of life are easy. A sound body also helps the brain use energy efficiently so that concentration and learning become easier.

Physical activity can also clear the mind of stress and depression, leaving peoplefeeling refreshed and invigorated. As a lifelong benefit, physical fitness may help people live longer by preventing ordelaying the onset of some diseases.

Q & AHow quickly will my body adapt itself to my new fitnessregimen? At the moment, I ache all over.

You may be doing too much too soon; slow down a bit. As you get fitter, you will be able to do more without feeling suchill effects. Your body has probablybeen underused for a long time;do not expect it to be in primecondition after only a few daysor weeks. There should not betoo much suffering involved in getting fit; more discomfortshould be felt during exercisethan afterward.

Are all children naturallyphysically fit or do they have to work at fitness?

The younger children are, theless they have to work at theirphysical fitness. As they growolder, however, the situationchanges; there will be anoticeable difference betweenthe performance of teenageathletes and their untrainedfriends. People from theirtwenties onward definitely need regular exercise for realfitness. Whatever one’s age, it is important to maintain fitness.

Physical Fitness

Football is an excellent way to keep physically fit.

155


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Lifestyle and physical fitnessIncreasing numbers of people are nowconcerned about physicalfitness, and manyindividuals participate in sports and physicalactivities as a matter of routine. Often, wholefamilies jog together, and jogging is one of the best activities for overallfitness. However, manypeople frequently embarkon a fitness program andthen give it up after a fewweeks. One reason is thatthey fail to realize that thecommitment to fitness is a lifelong contractbetween themselves andtheir bodies. They must

be prepared to persist so that physical activity becomes a habitand an enjoyable and fulfilling part of everyday life.

The first step is to choose enjoyable activities that fit easilyinto one’s lifestyle. Jogging or cycling to school, for example, may take only half an hour longer than the bus, but students will start the school day feeling much more invigorated. Dancingfor a couple of hours a week is another vigorous and healthyexercise that is happily and easily accommodated in people’slifestyle, whatever their age.

Developing lifelong habitsAt school, students should participate in sports that they enjoy,but they should remember that fitness for specific sports doesnot necessarily mean overall fitness. Some activities, such asgymnastics and karate, help muscular development andflexibility but do not fully exercise the heart and lungs in thesame way as aerobics does. Basketball and racquetball have arelatively high aerobic value, but many young people give upthese sports after high school or college. Unless they take upanother activity, they lapse into unfitness. It is a good idea totake up a lifelong sport, such as swimming or tennis, as part of one’s training and conditioning.

Physical Fitness

THE RIGHT CLOTHING

Loose, comfortable clothing thatwill not restrict movement shouldbe worn during exercising. Tightjeans and tops inhibit movement.Warm clothing is needed in coldweather to prevent tight, soremuscles and cramps. Layers ofclothing are best to soak up sweat.For joggers and runners, goodsneakers are vital. For skiers, good skis with efficient bindingsand automatic release in a fall are essential.

Basketball is the most popular sport inhigh schools in the United States. It helpsbuild muscles and is good for overallconditioning, because of its relatively high aerobic value.

Rollerblading is a good form of exercisethat can be enjoyed outdoors.


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Achieving maximum physical fitnessTo achieve maximum physical fitness, a combination of aerobicexercise and isotonic exercise should be undertaken. Aerobicexercise increases the amount of oxygen in the blood andprovides an improved oxygen supply to the body’s tissues,helping create a stronger heart and healthier lungs. Isotonicexercises develop muscular strength and flexibility. Aerobicexercise causes breathlessness, but if it is a regular activity, as performance time increases, so does the time beforebreathlessness starts. Cycling, running, swimming, and jogging are excellent aerobic activities.

Rowing, gymnastics, and skiing are sports with high isotonicvalue, as are exercise programs that include stretching, yoga, andweight training. Weight training should not be confused withlifting heavy weights. Weight training involves working out withlight weights of only 2 to 5 pounds (1–2 kg) to begin with andthen increasing the capacity to lift something a little heavier orfor a little longer. Weights help develop strength and enduranceand a firmer, leaner-looking body.

When both types of physical activities are combined with a healthy diet and plenty of sleep, peak condition is achieved.People embarking on such a regimen will have few weightproblems, will tire less easily, and will feel more relaxed and able to cope with mental activity.

Physical Fitness

EXERCISE SAFETY CODE

• Always warm up for 15 to 20minutes with basic calisthenics or stretching exercises.

• Stop when you are tired, andbefore you are exhausted.

• Stop if you are in pain.• Stop if you feel dizzy or

nauseated.• Take your pulse regularly.• Never exercise if you have a fever

or viral infection. • Always wear suitable clothing

for the type of exercise or sport.• Always cool down afterward to

relax and allow the pulse rate to return to normal.

Skiing is an excellent activity for keepingfit, but it is expensive and few peoplehave access to ski slopes all year round.


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A wide range of activitiesMany young people dislike organized sports and do their best toavoid them. Some have poor eyesight or are overweight. They feelthat they cannot compete with their more athletic peers. Othershave a disability, such as asthma or diabetes, which limits theiractivities. For those people who feel they cannot take part inregular fitness programs, there is a wide range of noncompetitiveor solo activities that can be fun and easily modified to suit the individual. A good example is swimming, which is a greatexercise for all-around fitness. It has high aerobic value, firms and strengthens the muscles of the lower and upper back, andstreamlines the whole body. Because water supports bodyweight, the effort of swimming seems less than it really is.

For asthmatic youngsters, swimming is an ideal activity thathelps them breathe more easily. It is important to note that foryoung diabetics, increased exercise must be balanced with an

Physical Fitness

RECOMMENDED WEIGHT FOR FEMALES AND MALESFemale

height

Small

frame

Medium

frame

Large

frame

Male

height

Small

frame

Medium

frame

Large

frame

4’ 8”

4’ 9”

4’ 10”

4’ 11”

5’ 0”

5’ 1”

5’ 2”

5’ 3”

5’ 4”

5’ 5”

5’ 6”

5’ 7”

5’ 8”

5’ 9”

5’ 10”

5’ 11”

6’ 0”

88–94

90–97

92–100

95–103

98–106

101–109

104–112

107–115

110–119

114–123

118–127

122–131

126–136

130–140

134–144

138–148

142–152

92–103

94–106

97–109

100–112

103–115

106–118

109–122

112–126

116–131

120–135

124–139

128–143

132–147

136–151

140–155

144–159

149–163

100–115

102–118

105–121

109–124

111–127

114–130

117–134

121–138

125–142

129–146

133–150

137–154

141–157

145–164

149–169

153–174

157–179

4’ 8”

4’ 9”

4’ 10”

4’ 11”

5’ 0”

5’ 1”

5’ 2”

5’ 3”

5’ 4”

5’ 5”

5’ 6”

5’ 7”

5’ 8”

5’ 9”

5’ 10”

5’ 11”

6’ 0”

101–109

104–112

107–115

110–118

113–121

116–125

120–129

124–133

128–137

132–142

136–146

140–150

144–154

148–158

152–162

156–167

160–171

107–111

110–121

113–125

116–128

119–131

122–135

126–139

130–144

134–148

138–152

142–157

146–162

150–167

154–172

159–177

164–182

169–187

115–130

118–133

121–136

124–140

127–144

130–148

134–153

139–158

143–162

147–166

151–171

156–176

160–181

165–186

170–191

174–196

178–201

Swimming is the best activity of all foroverall fitness. To get the most out ofswimming sessions, it is best to haveinstruction instead of just paddling up and down the pool.

This chart shows ideal weights (inpounds) for males and females. Bonestructure influences ideal weight; if aperson has a large frame, he or she willweigh more than a person with a smallframe, even if they are both the sameheight. If a person is too heavy or toolight and finds it difficult to reduce or gain weight, he or she may have aproblem that requires medical attention.


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increase in insulindosage, or hypoglycemicattacks will be likely tooccur. Their blood sugarlevels must be carefullymonitored.

Other activities thatcondition the body andare fun to do are dancing,roller skating, ice skating,cycling, hiking, andwalking. It is importantfor an individual tochoose an activity that heor she really enjoys andcan strive to be better at.

Cross-trainingOne problem with physical fitness activities is that young peopleoften are bored by a regular routine. This can be overcome bycross-training—adding something challenging and new to anexisting sport or activity. Cross-country hiking might make agood outdoor activity, or ice skating a good indoor one.

An individual could also combine walking with jogging, or slow walking with brisk walking. Someone who is a steadyrunner might enjoy a Swedish routine: instead of jogging at aneven pace, one can sprint, skip, jog, or walk to suit one’s mood.

Another great aerobic exercise is jumping rope. Steady rope-skipping is of greater aerobic value than jogging. The faster aperson skips, the faster the heart will beat. This is a good way of warming up on cold days. To avoid overstraining, a gradualbuildup is necessary with this activity.

Many people are attracted to martial arts, such as tai chi,karate, and kung fu (which combine mental and physicaldisciplines), and to yoga (which makes the body supple andrelaxes the mind). These activities add a spiritual dimension to fitness that many people find calming. New exercises andactivities help maintain fitness and activity throughout life.

Physical Fitness

aerobics • backache • blood pressure • diet • exercise

• food and nutrition • heart • isometric exercises •jogging • joint disorders • lethargy • muscle • oxygen

• sports • sports injuries • yoga

SEE ALSO

EFFECTIVENESS OF SPORTS AND ACTIVITIES FOR PROMOTING FITNESS

(ON A SCALE OF 1 TO 10)

Activity

Aerobic

benefit

Muscle

development Flexibility

BadmintonBaseballBasketballBicyclingCalisthenicsFootballGolfGymnasticsHandballHockey (ice)Horseback

ridingIce skatingJoggingJudoKarateRacquetballRoller

skatingRowing

Skiing (cross-country)

Skiing (downhill)

SoccerSoftball

(slow-pitch)SquashSurfingSwimmingTable tennisTennisWalkingWeight

lifting

7399574599

6910779

810

10

89

395

10587

4

6378894976

677787

610

9

96

3767576

10

84641054985

4741088

76

7

75

4868764

4

Ice hockey is an exciting sport and goodfor overall fitness, but protective gear isessential to avoid injury.


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Physical therapy is the treatment of disease, disability, and injuryby physical means, often in conjunction with drugs. It plays anextremely important part in rehabilitation. Physical therapyincludes exercise, massage, manipulation, and treatment withwater (hydrotherapy), heat, electricity, and ultrasound to restoreor maintain mobility and function. Therapists also teachbreathing techniques to prevent or alleviate chest infections.Most physical therapists are trained medical personnel who workin hospitals, but some therapists make house calls or work inclinics. Some therapists specialize in sports injuries and work in health clubs or sports clinics; others specialize in the care of handicapped children in special schools.

Manipulation, massage, and mobilizationThe techniques used in physical therapy are designed to improvethe functioning and increase the strength of various parts of thebody. In manipulation, finger and hand movements are used to apply pressure to make joints and tissues more flexible.Manipulation can help realign joints that are slightly out ofalignment, for example, and relieve pain where a nerve hasbecome pinched. A great deal of anatomical training is needed to know precisely where and how to apply this pressure.

In massage, the hands manipulate soft tissues around the joints to improve blood flow and help limb movement.Massage relieves muscle pain and helps the patient relax.Mobilization exercises help restore strength to weak muscles.

Hydrotherapy, heat, electricity, and ultrasoundHydrotherapy involves carrying out exercises in warm pools. Theheat of the water helps muscles relax and relieves pain. Paralyzedpeople particularly benefit from this treatment. The water givesthem buoyancy and a greatly increased freedom of movement,while the exercises strengthen their working muscles.

Ultrasound waves passed into the body help reduceinflammation and improve circulation. Infrared radiation, whichapplies local heat, also improves circulation and at the same timerelieves pain. Electric currents reduce pain, improve circulation,and help muscle contractions in diseased and injured limbs.

Q & AMy grandfather recently had astroke and has lost movementand feeling in his right arm. Howcan physical therapy help himwhen he cannot feel anything?

Physical therapists are trained totreat not only loss of movementbut also loss of sensation. Theywill be able to help yourgrandfather by retraining thenerve pathways that have beenaffected by the stroke to adaptto new patterns of movement.

PhysicalTherapy

Accustomed to exercise and freedom ofmovement, athletes are often frustratedby their slow recovery from injuries.Physical therapists have to be goodcounselors, too.

SEE ALSOcirculatory system • exercise • isometric exercises •joints • massage • muscle • pain • sports injuries


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Podiatry is a practice concerned with all aspects of the care of thefeet and with the treatment of commonly occurring minor footdisorders. Podiatrists (formerly called chiropodists) are medicallyqualified people who specialize in the diagnosis and treatmentof diseases and disorders of the feet.

Conditions treated by podiatristsCorns are protective responses to undue local pressure, usuallyfrom unsuitable footwear. The thickening and hardening of thesurface layers of the skin lead to a progressive worsening of thecondition, because the pressure forces the hard layer deeper intothe skin. Simply cutting off or softening a corn will not cure thecondition as long as the original cause persists.

In the case of plantar warts (warts on the sole of the foot), the pressure from body weight drives them inward. A podiatristrelieves pressure on the wart while local applications to destroy it are taking effect.

Bunions are also induced by pressure; in this condition,inflammation occurs in the protective, fluid-filled tissue bag(bursa) that lies over the side of the main joint of the big toe. Ifill-fitting shoes have forced the tip of the big toe toward the littletoe, the sharp angle formed will suffer increased local pressurefrom the shoe, and the bursa will be inflamed.

Podiatrists can also treat ingrown toenails. This condition isdue to pressure or injury that causes the nail to curve under andcut into surrounding tissue. It may also be due to infection thatcauses inflammation of the tissues at the edge of the nail. Thesetissues become swollen and overgrow the nail edge.

Onychogryphosis is abnormal thickening of the toenails. It maybe due to fungal infectionof the nail or to repeatedinjury. Fungal infection ofthe nails is common butdifficult to cure.

Other conditionscommonly treated includeflatfoot, athlete’s foot,hammertoe, curly toe,clubfoot, ulceration fromvaricose veins, and gout.

Q & AI was sick recently and had tospend a lot of time in bed. Nowthat I’m able to get up, my feetare flat and painful to walk on. Is this permanent?

No. This is a temporary condition.Because you have not been usingthe muscles in your feet, theyhave become flabby and weakand cannot support the arches. A podiatrist can give you somefoot exercises to strengthen themuscles and help build up thearches.

I am training to be a balletdancer. I have constant problemswith my feet, especially bunions.What can I do to prevent orreduce the effects of strain onmy toes?

It is important for you to see apodiatrist regularly, especially ifyou are planning to have a careerin ballet. The podiatrist willcheck to see that your balletslippers fit correctly and willadvise you on general foot care.

Podiatry

The big toe is turned at an extreme angle,causing deformity of the bone. The softtissue around it has thickened to form a painful bunion. A podiatrist will carryout surgery to rectify these conditions.

athlete’s foot • feet • joints • muscle • sports injuries

SEE ALSO


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Posture is the term for the way people stand, sit, and move. In anupright position, the body’s center of gravity (where the weight is balanced) is on the lower back and hips. Good posture involvesmaintaining the balance of body weight around this area, evenwhen people walk, sit, run, work, or play games.

Many people who do not lead active lives have poor posture.Sitting hunched over a desk or at the wheel of a car throws thebody weight forward onto the upper spine and shoulders. Manychildren develop bad posture as they are growing. Boys and girlswho are taller than their friends often droop the head and chestand slouch instead of standing up straight.

Achieving good postureGood posture is not hard to achieve, and a series of simpleexercises can help correct bad posture. Dancing, yoga, and body-conditioning systems, such as Pilates or the Alexandertechnique, can also help. The ideal posture is a straight spinewith the back of the shoulders and the back of the buttocks in line. The shoulders should be relaxed and drawn gently back,with the eyes looking straight ahead. It may help to imagine astring coming out of the top of the head and being pulled up;this is the body’s natural alignment. It is also best to relax a little to avoid looking stiff. The posture will then improve and

people will begin to move more gracefully.

A great benefit of goodposture is that it makespeople look and feel good. Dancers, models,and actors are aware ofthis; they look betterwhen they stand andmove well. Anotherbenefit is that peoplewith good posture aremuch less likely to sufferfrom complaints such asbackache and arthritis as they grow older.

Q & AIs the traditional military-styleposture still the best?

In general, yes. The ideal is astraight spine with the back of the shoulders and the back of the buttocks in line, theshoulders drawn well back, and the chest pushed slightlyforward. The chin should betucked in and the eyes should be looking straight ahead.

If you have bad posture whenyou’re young, will it cause backtrouble when you’re older?

Yes. All the joints of the bodysuffer wear and tear over theyears, but the joints in the feet,ankles, knees, hips, and lumbarspine are under even greaterstrain, because they have tosupport the whole weight of the body. In later life, these jointsare the most likely to becomepainfully arthritic. You can helpprevent this by keeping yourweight down and maintaininggood posture.

Posture

alexander technique • arthritis • backache • hip • joint

disorders • physical fitness • scoliosis • shoulder •skeletal system • spinal column • yoga

SEE ALSOThis girl may be an excellent student, but sitting hunched over her work will make her feel tired and may causecurvature of the spine. It is always best to sit upright at a desk when studying.


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Q & AMy friend says that she wants tocut out proteins from her diet.What happens if a persondoesn’t eat any protein?

Protein is an essential part of thediet. If people are starving, theyusually do not have enoughprotein or energy-producingfood, so the body breaks downits own protein to act as a fuel,losing much muscle bulk. Lack ofprotein in a normal-calorie dietleads to a condition calledkwashiorkor, which occursmainly in young children.

Is protein the best sort of food to eat if I want to put on weightand build myself up?

If you want to build up yourbody’s muscle content andstrength, the best way is toexercise to encourage themuscles to grow. Simply eatingmore protein is an expensiveway of putting on fat.

Protein

The amount of protein in certain foodscan come as a surprise. Dried soybeans,for example, contain more protein weightfor weight than a prime cut of beef.Cheese, lentils, and oily fish such asmackerel and herring are also excellentsources of protein.

body systems • calories • carbohydrates • diet •dieting • fats • food and nutrition • malnutrition •nutritional diseases • obesity

SEE ALSO

Protein, contained in foods such as meat, fish, dairy products, andbeans, is an important part of the diet. Although protein can beburned in the cells simply as fuel (energy) in the same way asfats and carbohydrates, it has a far more important role. Proteinis essential in maintaining the body’s continuing process ofrepairing and rebuilding cells in the body, so that the bones,muscles, and tissues remain in a healthy condition.

Proteins are the body’s building blocks and play a vital role in the overall function of the body. Tissues are basically made of protein; the substance that holds together the organs andtissues is a type of protein called collagen; enzymes are made of proteins; and proteins are present both in the blood and inhormones. Proteins are made from amino acids. Different kindsof proteins are combinations of some of the 20 different types of amino acids. The genetic code—which determines everythingfrom a person’s hair color to inherited talents—instructs the cells how to combine the amino acids to make proteins. Thebreakdown and buildup of new protein take place in the body all the time. The entire protein structure of the body is renewedevery 60 days. The blood, liver, and other tissues are renewed byfood and recycled body proteins.

A high-protein diet is particularly important for babies andchildren, whose bodies are growing quickly. A baby gets most of its protein from milk. An adult, however, needs less protein.


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Puberty is the name given to the age when children start tobecome sexually mature. The period from puberty to maturity is called adolescence. During this time, boys and girls go througha number of physical and emotional changes.

Hormonal changesPuberty is triggered by hormones from the pituitary gland at thebase of the brain, which causes changes in the adrenal glandsand in the ovaries and testes. In girls, the pituitary gland beginsto secrete a variety of stimulating (tropic) hormones, under theinfluence of another part of the brain called the hypothalamus.These hormones travel to other hormone-secreting (endocrine)glands, which then release other hormones that directly affectsexual development.

Tropic hormones in the ovaries trigger the production of the hormones estrogen and progesterone. In turn, thesehormones initiate and maintain the menstrual cycle. Along with the hormones released by the adrenal glands, estrogen and progesterone cause changes in a girl’s body shape and stimulate other secondary sexual changes.

As in girls, the pituitary gland is responsible for starting andcontinuing the changes in a boy’s body during puberty. Spermproduction is triggered by the action of the tropic hormones on the testes, stimulating the release of the hormonetestosterone. Testosterone, along with other hormones from the adrenal glands, causes other secondary sexual developments,such as rapid growth, a deepening voice, and a broadening of the shoulders.

Physical changesPuberty in a girl may begin as early as age 9 or 10, or be delayeduntil 15 or even later. Changes in a girl’s breasts are an early signof puberty. Hair begins to grow in the pubic region and in thearmpits. As she grows taller, the hips, thighs, and buttocks growcomparatively larger and the waist becomes more defined. Theoil-producing glands in her skin become more active, possiblyleading to greasy hair and skin.

After some of these changes, a girl will have her firstmenstrual period. At first, the periods may be slight and come at irregular intervals, but after a year or so, they should settledown to a regular cycle of about 28 days.

Boys usually begin puberty around the age of 13, although it may be as late as 15, with the first ejaculation of semen. Duringa boy’s growth spurt, his legs grow longer, the body’s trunkbecomes longer and broadens, and the muscles develop. An

Q & AMy brother has hit puberty and now just stays in his room playing music. He hardlytalks to anyone in the family at all. Should our parents makehim spend time with the rest of the family?

Privacy is very important to some adolescents. It gives them the chance for individualmental development and lateremotional balance. Your parentsshould try to be sympathetic to your brother’s needs but make it clear to him that theyare there for him and are willingto discuss any worries he mighthave. You will find that gentlecoaxing will be more effectivethan an argument.

Is chubbiness during pubertycaused by malfunctioningglands?

Very rarely. Usually chubbiness is due to a lack of coordinationbetween appetite and need.When children are growing fast,usually between ages 11 and 17,they need more food than beforethey started puberty. The troubleis that when this growth spurtslows down, the appetite doesnot always readjust.

Puberty


165

obvious change is the deepening of the voice. Hair begins togrow in the pubic region and in the armpits, and later on theupper lip and chin. At this time, many boys and girls develop thehabit of masturbation. Boys have nocturnal emissions of semenin their sleep, often associated with sexual dreams. Such dreamsare normal. Boys, like girls, tend to develop oilier skin and hair and some develop acne due to hormonal changes.

Many girls and boys have mood swings; they are self-consciousand preoccupied with their looks and with their relationships.Some immerse themselves in sports or schoolwork and avoid the opposite sex, who can make them feel unsure of themselves.A great deal of anxiety can be spared if girls and boys know inadvance what is happening to them.

Puberty

The bodily changes that take place in a girl during puberty can start as early as 9 or 10. The girl shown here has startedto develop pubic hair and breasts at thesame time. This is not always the case.Often breast development outpaces hairgrowth in the armpits and pubic region.The illustration charts the progress of a developing girl over a period of aboutfive years.


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Puberty

The bodily changes that take place in aboy during puberty can start as early asage 13. Once puberty begins, a boy’s bodygradually changes shape. The boy alsostarts genital development and pubic hair growth. This illustration charts thedevelopment of a boy from about age 10to age 16.

SEE ALSOanorexia and bulimia • body systems • diet • dieting •exercise • food and nutrition • glands • growth •muscle • physical examination • physical fitness •posture • skeletal system • skin • sports • weight

control


167

When a person touches a stove that is very hot, his or her handmoves away at once. If there is a brilliant flash of light, a personblinks. These are examples of reflex actions. Reflexes areautomatic responses of the body to outside influences. They are not under conscious control.

New babies have several reflexes. For example, if someonegently strokes around the mouth of a newborn baby with onefinger, the baby will try to suck the finger.

Many reflexes are learned, such as avoiding a hot stove. Some learned reflexes are known as conditioned reflexes. In a conditioned reflex, the desired reaction is brought about by a stimulus that is different from the stimulus that originallycaused the reaction.

A Russian psychologist, Ivan Pavlov (1849–1936), was the firstperson to discover conditioned reflexes. Pavlov found that if herang a bell every time he gave a dog a scrap of food, after a while the dog would salivate if Pavlov merely rang the bell without any food being in sight.

Q & ADo young babies have a sucking reflex or do they learn to suck?

Babies are born with a suckingreflex. If you gently stroke thecheek of a newborn baby nearthe mouth, his or her head will turn toward your finger.Once the finger is in his or her mouth, the sucking reflex is stimulated. The reflex is lost as the child grows.

I find myself blinking a lot when I walk into a strong light.Is the blinking a reflex?

Yes. Strong light will cause areflex blink, giving the pupil a chance to constrict (again by reflex). Blinking avoidsoverstimulation of the retina,which might otherwise bedamaged by excessive light.

My friend says that it’s possibleto stop reflexes from occurring.Is she right?

Yes and no. For example, simple tendon reflexes can be inhibited by tensing themuscles. Others, such as the choking reflex, cannot be stopped at will.

Reflexes

By striking just below the knee witha tendon hammer (right), thedoctor can test muscle reflexes.

Blinking (below) is a reflex actionthat protects the retina from strong light.

knee • muscle • nervous system • pain • tendon

SEE ALSO


168

All body cells need a constant supply of oxygen to survive and todispose of a waste product, carbon dioxide. Both requirementsare fulfilled by the respiratory system and the circulatory system.The two systems deliver oxygen from the lungs to the cells andremove carbon dioxide from the cells for return to the lungs,where it is exhaled. This exchange of oxygen and carbon dioxidebetween the air, blood, and tissues of the body is known asrespiration.

When air is breathed in, it is taken to the lungs. There, theoxygen it contains is exchanged for carbon dioxide, which, withwater vapor, is expelled when people breathe out. This process is controlled by nerves that automatically send impulses to themuscles, so that people breathe in and out in an involuntary way.

Air is drawn into the body through the nose and mouth andtravels down the throat (the pharynx and larynx) and thewindpipe (trachea). The windpipe divides into two branchescalled bronchi, each leading to a lung.

How the respiratory system worksThe lungs are like a pair of bellows in the chest. Around them arethe rib cage and the rib muscles. Below them is a sheet of musclecalled the diaphragm. The rib cage, muscles, and diaphragm formthe chest cavity. When the diaphragm contracts and the chestwall rises, the space in the chest increases and air rushes into the lungs. When the muscles relax, the lungs, which are naturallyelastic, collapse and air rushes out.

From the nostrils to the lungs, the air is warmed, moistened,and filtered. Tiny hairs covered with mucus line the passages andtrap as much dust and germs as possible when they enter thesystem. However, these hairs cannot cope with cigarette smokeor very polluted air. If a large particle enters the system, it iscoughed out or sneezed out. Food is prevented from entering therespiratory system by the epiglottis, a flap of tissue that closesoff the windpipe as the food passes into the gullet.

The air travels into the bronchi and then into even smallerbranches called bronchioles. At the ends of these narrow tubesare minute air sacs called alveoli. The alveoli are covered with a network of tiny blood vessels called capillaries. The exchange of gases—oxygen for carbon dioxide—takes place through thewalls of the alveoli, which are fused with the capillary walls.

The red blood cells contain hemoglobin, a compound thatpicks up the oxygen from the lungs. The hemoglobin carries theoxygen to every cell in the body and releases it. At the same time,carbon dioxide passes into the blood and is carried back to thelungs, where it is breathed out.

RespiratorySystem

Q & AMy brother has been diagnosedas having small lungs. Is thisserious?

Each lung has a capacity ofaround 0.09 cubic foot (2.5 l), but the amount of air passing in and out is often only a tenthof this, so your brother should be all right. Many peoplemanage with only one lung.

Why are singers taught tobreathe from the diaphragm?

The diaphragm controlsbreathing rate and depth. A voiceteacher helps students developtheir abdominal muscles tocontrol their diaphragm so thatthey can hold long notes andcreate vibrato.

I broke my ribs playingbasketball. Why was I notbandaged or given any treatment?

Although broken or cracked ribscan be uncomfortable or painful,the main danger is that thechest movement will be reduced,producing less airflow into andout of the underlying lung. Thiscan cause pneumonia, so it isunusual to bandage broken ribs.


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Respiratory System

Air (1) inhaled via the trachea (windpipe), bronchi, andbronchioles reaches the alveoli, where oxygen from theair is transferred to the capillaries surrounding eachalveolus (2). The oxygenated blood is carried by thepulmonary veins (3) to the left side of the heart andpushed into the aorta (4), which is the body’s main artery.Blood then travels around the body through the arteriesto the capillaries (5). The oxygen carried by the red blood

cells is given to the body cells, which transfer their wasteproduct, carbon dioxide, to the fluid of the blood (6). Thisblood is carried back through the veins (7) into the rightside of the heart. Finally, the blood flows through thepulmonary artery (8) into the lungs. At the site of thealveoli (2), the circulating blood gives up its carbondioxide, which is exhaled (9), and then takes in oxygenagain (1). The cycle then repeats itself.

bronchus

vein

aorta

heart

trachea (windpipe)

airflow into and out of the body

aorta

pulmonary artery

left pulmonaryveins

right pulmonaryveins

red blood cellscarrying oxygen

capillary

flow of oxygen into body cellsflow of carbon dioxidefrom body cells

lung

bronchiole

alveoli

alveolus

network ofcapillaries

hollow centerof alveoluscontaining air

blood flow intoand out of alveoli

91

4

8

3

3

7

2

4

5

6

asthma • autonomic nervous system • body systems •circulatory system • heart • hyperventilation • muscle

• nervous system • oxygen

SEE ALSO


170

Rest and relaxation are ways of recharging the body’s batteriesand guarding against stress. Knowing how to relax by getting ridof mental and physical tension is essential to good health. To stayhealthy, a person needs to relax mentally and physically. It isdifficult for people to achieve their goals if they are so tense thatthey suffer from stress, or so tired that they cannot move awayfrom the television.

The best way to relax is to be active. The more exercise onegets, the less tired one will feel. The body will also be in goodshape, and any emotional and psychological problems that may have been present will become less intense. Jogging andswimming are especially good for lifting a person’s mood. Ifpeople feel tired or exhausted, they should not head for therefrigerator for a sandwich; instead, they should go to the gym or do some other type of exercise.

Importance of sleepBeing tired from intense physical activity helps people get properrest when they need it. Young people particularly find it difficultto get out of bed in the morning. Seven or eight hours’ sleep is all that is needed. If people go to bed at a reasonable time, theyshould wake rested and refreshed in the morning. Staying uplate—studying or partying—means that people are still tiredwhen they wake and will be unable to concentrate or enjoy the next day’s activities.

Avoiding tension by learning to relaxEveryone has to cope with some tension in life. At school, work, or home people constantly experience fear, anger, guilt, overwork,and worry. Some of this tension is necessary if people are to meet

Q & AHow can I relax and still remainalert while driving?

If you have had an exhaustingday, pause a few minutes in the driver’s seat before you turnon the ignition. Relax all yourmuscles in turn, and make sureyour back is well supported. Lean back when you are driving;do not hunch over the wheel. At stoplights or when you are in dense traffic, check again that your muscles are relaxed.

How can I be, and appear, morerelaxed during an interview foran after-school job?

Tension is unavoidable during an interview, and one of theaspects of the interview is forthe employer to see how youperform in a tense situation. To appear at ease, sit with yourback against the back of thechair, relaxing your shoulders.Keep your feet still and yourhands folded in your lap. Do notfold your arms across your chestor lean too far back in your chair.

Rest andRelaxation

Regular exercise keeps people in goodphysical condition and has the addedadvantage of giving them time to relaxand escape from worries.


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challenges and achieve ambitions. However, if too much tensionbuilds up, without periods of relaxation, there is a danger ofmental illness or the development of a physical problem.

The body’s response to relaxationWhen people are properly relaxed, a number of changes takeplace in the body. The heartbeat decreases and breathingbecomes slower. The brain-wave patterns are changed andpeople become more aware of their body and thoughts.

If people suffer from tension, for example before an exam or an interview for a job, they should make a conscious effort to relax the muscles one by one and to clear the mind ofconflicting thoughts. Books about relaxation can be found in local libraries or bookstores.

Relieving mental stressPeople who suffer from fear, phobias, depression, and other mental problems often benefit from special relaxation programs.They learn simple relaxation techniques, such as deep breathingand how to reduce muscle tension gradually.

Some people find that yoga, meditation, or massage areeffective activities in reducing fears and worries, and afterwardthey feel rested and revitalized.

Rest and Relaxation

Many people find that one of the bestways to unwind is to relax in a quiet,comfortable room at home. Even a rest of only 15 to 20 minutes helps relievetension.

Sometimes it is enjoyable doing nothing.It can be restful and relaxing and canmake a positive contribution to goodhealth. However, such relaxation shouldalso be balanced by activity.

SEE ALSOexercise • isometric exercises • jogging • lethargy •massage • physical fitness • sports • tiredness • yoga


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Salmonellosis is a common form of food poisoning, caused bybacteria of the genus Salmonella. These organisms contaminatefoods from domestic animals, especially eggs, poultry, meats, and dairy products, as well as fish and shellfish. Salmonella isconsidered one of the nation’s most important communicablediseases, affecting approximately two million people each year.

Bacteria killed by heatSalmonella bacteria are killed by heat. Freshly cooked food that has been heated through quite thoroughly should be safe. However, unless the cook is hygienic, the food may becontaminated again by coming into contact with raw meat,kitchen utensils, or hands. Cooked and raw food should always be kept separate. Freezing does not kill salmonella; it simplystops bacterial growth, which will begin again as the food thaws. Frozen poultry is easily contaminated as it is prepared for freezing; it must always be thawed out completely beforecooking, and then cooked thoroughly all the way through.Undercooked eggs, or foods such as mayonnaise that are madewith raw eggs, may also carry the infection. These types of foodsshould not be given to those who are in at-risk groups, such aspregnant women, babies, young children, people with immunedeficiency diseases, and seniors.

Some household pets, such as chicks, frogs, and aquariumsnails, can pass on salmonella bacteria. Infection can be avoidedby careful hygiene. The hands should always be washed afterhandling aquarium pets, and pet birds should be kept out of the kitchen or other rooms where food is usually prepared oreaten.

Symptoms and treatments Symptoms of salmonella poisoning include severe headache,vomiting, diarrhea, stomach cramps, and sometimes fever.Treatment is usually bed rest with a diet of bland food and plenty of fluids. Patients at risk are often prescribed antibiotics.

Epidemics of salmonella poisoning can be particularlydangerous in nursing homes, where the elderly patients arevulnerable to it. Public health regulations aim to preventoutbreaks by overseeing standards of hygiene in foodpreparation factories, hospitals, restaurants, and hotels.

Q & AI read somewhere that the acid in a person’s stomachdestroys salmonella. If this is true, then how do peoplemanage to get infected with salmonella?

It is certainly true that stomachacid provides an importantbarrier to infection. Food tendsto stay in the stomach longerthan liquids, so an infected drink may be a greater hazardthan infected food. It alsoappears that people with nostomach acid (as a result ofeither illness or an operation) are more at risk of being infected by salmonella.

Salmonella

Cooked meat can be contaminated withbacilli from raw meat. The salmonellabacterium seems to thrive in poultry and eggs and in processed cooked meatsprepared in unhygienic conditions.

digestive system diseases and disorders • food poisoning

SEE ALSO


173

Salt is essential to life. It plays a part in stabilizing the body’s acid and alkaline balance; helps in the maintenance of muscles,nerves, and blood; and, with potassium, regulates the body’sinternal fluid supply. Salt is a compound of sodium and chlorineand is naturally present in most of the foods eaten. However, inthe United States and elsewhere in the developed world, peoplehave become accustomed to well-salted food. Salt is also addedto meat and vegetables in the cooking process. There areextremely high levels of salt in foods such as processed potatochips, peanuts, snacks, and other junk foods. Surprisingly largeamounts of salt are hidden in breads, cereals, and canned foods.

Nutritionists agree that people eat too much salt and that this could be the cause of a number of conditions, such as fluidretention, kidney disorders, and even muscle damage. Many ofthe symptoms of premenstrual syndrome are in part due to theretention of salt and water in the body. Salt has also been linkedwith migraine headaches. Excessive salt can cause hypertension(high blood pressure) in some people, which may lead in turn toheart diseases and strokes. Populations that eat low-salt dietshave a much reduced incidence of hypertension.

People should cut down or give up salt to minimize the risks of disease in later life. In cooking, it is best to season food onlywith spices, herbs, garlic, and lemon juice to add flavor.

Q & AIs it true that too much saltcauses high blood pressure?

The exact cause of high bloodpressure is not known, but it is likely to be due to a fewfactors, including heredity. There is also some evidence to suggest that salt may be animportant factor. For example,the disease is more common in countries where there is ahigh salt intake. There is littledoubt that the body’s salt-retaining mechanisms areinvolved in setting the level of blood pressure higher thannormal. Very low-salt diets canalso be successful in lowering blood pressure.

I often get cramps in my legs at night. Could this be caused by a lack of salt?

Probably not. Severe salt loss canbring about cramps, but this isunlikely in a temperate climate.Night cramps are common andcan be alleviated by takingquinine pills before going to bed.

Salt

Athletes need more salt in their diets,because they lose a great deal of salt andfluid through sweating, both of whichneed to be replaced to avoid dehydration.

SEE ALSOdiet • food and nutrition • minerals • muscle diseases

and disorders • nutritional diseases • stroke


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Sciatica, or sciatic neuritis, is pain along the large sciatic nervethat runs from the lower back down through the buttocks andalong the back of each leg. It is a relatively common form of backpain. The pain is caused by pressure on the sciatic nerve as itleaves the spinal column. Sciatica can have a variety of causes,including a herniated (slipped) disk in the spinal column,arthritis, or a fall. In most people who have sciatica, the disks inthe backbone have become weakened, either with age or as aresult of excessive strain. The disks are pads of tissue thatseparate the vertebrae. The disks and vertebrae provide thenecessary flexibility for people to stretch and bend. Each diskconsists of a soft center, which acts as a shock absorber, and atough fibrous outer layer. Sometimes, this outer layer weakens inparts, and the soft center bulges out. The resulting bulge putspressure on the nerve to the leg and causes the pain of sciatica.

Any pressure on the sciatic nerve causes sharp, stabbing painsin the buttock and down the leg. It may happen suddenly whensomeone is bending or stretching or it may come on gradually.Even a slight movement, such as coughing or sneezing, can bringon the pain or make it worse. For anyone suffering from sciatica,walking and sitting can be painful and difficult. The mostcomfortable position is lying on the back with the knees bent.

TreatmentsSciatica as a result of a slipped disk, which can be extremelyunpleasant on some occasions and often disabling, usuallyimproves on its own if the proper measures are taken. Treatmentfor sciatica starts with relieving the pain by resting in a firm bedand taking painkillers when necessary. Manual treatments, suchas physical therapy and osteopathic or chiropractic treatments,may help relieve the pressure. Painkillers such as nonsteroidalanti-inflammatory drugs (NSAIDs), oral steroids, or epiduralsteroid injections can help relieve the inflammation. Musclerelaxants may be used to help relieve spasms.

It is very important to stay in bed and to resist the temptationto be up and about when the disk is only half-healed; otherwise,the patient will be back to where he or she started. Surgicaltreatment, a last resort, is usually reserved for those who have had repeated episodes that have not improved with bed rest.

Q & AI’m very confused. What is thedifference between a backacheand sciatica?

Sciatica is the name given to the type of back pain thatradiates down the back of the leg. However, herniated(slipped) disks may start withpain limited to the back beforethe disk starts exerting pressureon the nerves to the leg, whichcauses sciatica. Most people witha bad back do not have slippeddisks; they have strainedligaments and muscles.

I’ve heard of some people who had surgery to cure their sciatica, but that soundsextreme to me. Is surgery always necessary, or are there other ways to curesciatica?

For a person’s first attack of sciatica, the doctor will probably not recommendsurgery so long as he or she is fairly confident that a slipped disk is the cause (as it usually is). Most peoplewith sciatica find that the pain improves if they can resttheir back properly and thenresume exercise.

Sciatica

SEE ALSOchiropractic • leg • nervous system • pain • physical

therapy • slipped disk • spinal column • spinal cord


175

Any sideways curvature seen or felt in the spine (spinal column)is called scoliosis. However, the spine is very flexible, especially inchildhood, and it is easily bent to one side. A normal spine shouldappear straight when viewed from the back. There are otherforms of spinal curvature, including kyphosis (a rounded back)and hunched shoulders in people who have poor posture.

There are two types of scoliosis, postural and structural.Postural scoliosis happens when something other than the spinecauses it to bend to one side: for example, having one leg shorterthan the other. When a child is sitting, however, the spine isstraight. This test distinguishes postural scoliosis from thestructural form. Many children have slight postural scoliosiswithout being aware of it. Older people with a slipped disk may have tight muscles on one side of the spine, which can also cause temporary postural scoliosis.

In structural scoliosis, there is a permanent defect in the bonesof the spine or in their relationship to each other. In addition,because there is a fixed abnormal curve, there will always be asecondary curve to compensate so that the shoulders remainstraight. The most common type of structural scoliosis isadolescent idiopathic scoliosis, which occurs while the spine is growing. The cause is unknown. It is usually first noticedbetween the ages of 10 and 15 and may affect any part of thespine. If the scoliosis is in the chest region of the spine, the ribswill protrude on the side of the curve and cause a hump. In girls,the breasts may also appear unbalanced.

Other types of structural scoliosis may be due to bone disease,bone abnormalities present from birth, or unbalanced muscledisorders that cause a sideways pull on the spine.

TreatmentsFirst, the type of scoliosis must be diagnosed. X-rays are takenof the spine to measure the angle between the upper surface ofvertebrae above and below the scoliosis. Regular checks areneeded to monitor the condition. Exercises may be helpful formaintaining the flexibility of the spine, but they cannot curescoliosis. If the curvature gets worse and the angle exceeds 20 degrees, a spinal support is required until the bones havestopped growing. When the curvature is more than 40 degrees,surgery is required to straighten the spine and fuse the bones.

Q & AMy 10-year-old-brother hasscoliosis. The doctor says that my brother may need an operation when he is older but must wear a brace until then. Why?

Scoliosis tends to worsen during growth, so your brotherprobably needs a brace toprevent his curve from gettingany worse. Operations forscoliosis stop the spine fromgrowing, so surgeons prefer to put off the operation until the child’s growth is nearlycomplete.

SEE ALSOarthritis • backache • exercise • growth • posture •slipped disk • spinal column • sports

Scoliosis

The effects of scoliosis—a twisted spine—can be clearly seen in this woman.


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Scurvy is a disease caused by severe vitamin C deficiency. Thisvitamin is present mainly in fresh fruits and vegetables. Indeveloped countries, scurvy is uncommon, but elderly people,alcoholics, and anyone who does not eat properly may develop it.

Vitamin C is needed to produce collagen, which is the basicprotein that makes up all fibrous tissues in the body. Vitamin C is essential for the formation of blood vessels, bones, teeth, andligaments. If there is insufficient vitamin C in the diet, bloodvessels weaken and may bleed and other collagen problems may arise. Vitamin C is also an important antioxidant, asubstance that helps reduce the risk of tissue damage frompowerful chemical groups called free radicals. Free radicals are implicated in many disease processes and other healthhazards, such as smoking, and are thought to be involved in the deposition of cholesterol in the arteries.

Children who do not have enough vitamin C lose weight andbecome irritable, their gums bleed, and their limbs may swell and become painful. Adults with scurvy also lose weight andbecome depressed. Their gums bleed and then draw back fromthe teeth, which may fall out. Large bruises appear, usually on the thighs, and sometimes there are little red bleeding marksaround the roots of body hairs. As the disease gets worse, there is bleeding in the muscles or in the intestines. Wounds may not heal, because vitamin C is essential if the skin is to healproperly. The bones may become softened due to the deficiency.

Treatment for scurvy is simple—vitamin C tablets bringimmediate improvement; then the patient must keep to a diet that contains enough vitamin C.

Q & AIs scurvy an extremely painfulcondition?

If the teeth are still present in the mouth, it can be verypainful. The pain of scurvy ismost striking in babies. Thedisease causes bleeding into the periosteum, the fibrouscovering of the bones, and this condition is so painful that the baby may adopt thecharacteristic froglike postureassociated with scurvy.

I understand that scurvy causes the teeth to fall out, but what happens if a personhas already lost all of his or her teeth?

One of the main effects of scurvy is on the teeth and gums, which bleed and becomeinfected. If the person hasalready lost his or her teeth, the gums will not be affected.

Is there vitamin C in potatoes?

Yes, but the amount variesaccording to how long they have been stored. New potatoescontain more vitamin C thanolder potatoes. Also, prolongedcooking destroys the vitamin.

Scurvy

Scurvy was once a commondisease among sailors whowent on long ocean voyages.However, once it wasrecognized that eating freshfruits and vegetables couldprevent scurvy, such supplieswere carried on boardwhenever possible.

aging • antioxidants • bruises • cholesterol •circulatory system • diet • digestive system • food and

nutrition • ligaments • muscle • nutritional diseases •protein • skin • vitamins

SEE ALSO


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A shoulder is a joint that connects the arm to the body. A ball-shaped projection at the top of the humerus (upper arm bone)rests in a rather shallow cup in the scapula (shoulder blade). This ball-and-socket joint allows the arm to rotate through a complete circle in several planes. No other joint in the body has this range of movement.

The ligaments that hold the shoulder joint in place are notparticularly strong, and that is why people often dislocate theirshoulders. However, the muscles that control the shoulder’smovement help make the shoulder joint stable. The mostimportant muscles are the series of fan-shaped muscles that run from the scapula to the top of the humerus and to the end of the clavicle (collarbone).

Q & AMy teenage brother tends to walk and sit badly, with his shoulders permanentlyrounded. Is there any medicalreason why he should beencouraged to improve hisposture?

Yes, definitely. Sitting andwalking with rounded shouldersmay give rise to a permanentdeformity and is often associatedwith pain and disability of thearms and hands. In addition, your brother’s round-shoulderedstance may reflect an excessivedegree of self-consciousness,which is a common problem of adolescence.

Why is it that after a goodnight’s sleep I often wake upwith a pain in my shoulder?

When you sleep soundly and do not move about much in bed, certain muscles, dependingon the exact position in whichyou are lying, tend to stiffen up and the nerves in that areamay be subjected to abnormalpressure. For both reasons, pain can result. Try to do someloosening-up exercises in themorning. If the pain persists,consult your doctor.

Shoulder

exercise • joint disorders • joint replacement • joints •ligaments • muscle • skeletal system • sports injuries •tendon • tennis elbow

SEE ALSO

The shoulder is a ball-and-socket joint. The head of theupper arm bone, or humerus,sits in the shallow socket of the scapula, or shoulderblade. A special fluidcontained in the synovialcapsule protects andlubricates the joint. Theligaments and muscles hold the humerus andscapula in position.

trapezius

deltoid

greater pectoral

biceps

clavicle

ball-and-socket joint

scapula

humerus


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The human skeleton is strong enough to keep the body uprightand protect vital organs, yet it is flexible enough to allow greatfreedom of movement. The skeletal system consists of theskeleton itself, which is made of bones, and the related cartilage,ligaments, and muscles.

An adult’s skeleton has 206 bones. As a child grows, manybones—for example, those in the skull—fuse together. Male andfemale skeletons have the same number of bones, but in generalthe female skeleton is smaller and lighter. A woman’s pelvis is broader and more boat-shaped, giving the hips theircharacteristic shape and allowing room for the passage of a baby’s head during childbirth. A woman’s shoulders are relativelynarrow. In a man, the general proportions are reversed: broadshoulders and slim hips.

Each part of the skeleton has a different function. The skullprotects the brain, the middle ear, the inner ear, and the eyes. Thespinal column (backbone) protects the spinal cord and is madeup of a chain of small bones, rather like spools, called vertebrae.Its structure gives the spinal column enormous strength, but atthe same time it is very flexible. The rib cage, made up of thebackbone, sternum (breastbone), and ribs, protects the heart andlungs. The pelvis shields the reproductive organs and the bladderand serves as an anchor point for the legs.

CartilageCartilage is a smooth, tough, flexible tissue that forms part ofthe skeletal system. It is composed of cells surrounded by fibersof collagen and elastic. Cartilage gives the body strength andelasticity. There are no blood vessels or nerves in cartilage.Instead, food and oxygen are diffused from the surroundingtissue fluid.

The structure of cartilage varies according to its function.Yellow, or elastic, cartilage is extremely flexible and occurs in theearlobes, tip of the nose, and voice-producing part of the larynx.Fibrous cartilage forms the shock absorbers in the knees and thedisks between the vertebrae in the spine. Hyaline cartilage linesthe movable joints of the body.

OssificationNearly all bones begin as rods of cartilage that are graduallyhardened by deposits of calcium and other minerals. This processof hardening is called ossification. It begins in the third or fourthmonth of an embryo’s life and continues until about the age of21. With age and wear and tear, cartilage can cause problems,particularly in the spine and knees.

Q & AHow much force is needed tobreak a bone?

That varies according to theposition, shape, and health ofthe bone. The long thin bones of the arms and legs are moreprone to snapping fractures than are the plate bones of the shoulder and pelvis (whichare more prone to heavy blowsor crushing injuries). People who are undernourished, andolder people whose bones have lost part of their proteinframework, have brittle bonesthat break easily. This isparticularly the case withmenopausal women who have osteoporisis.

What is a greenstick fracture?

Instead of the bone breakinginto two or more separatefragments, only one side of it breaks. The other side is more bent than broken. Theappearance and effect aresimilar to what happens if you try to break a stick of woodthat is still green, hence thename. These fractures usuallyoccur only in children whosebones have not yet fully ossifiedand are thus more supple.

Skeletal System


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Skeletal System

The human skeleton, made up of morethan 200 rigid but living bones, supportsthe body and its vital organs and providesits shape. Here, the major bones of theskeleton are identified.

Skeletal developmentA newborn baby has more bones in its body than an adult. Atbirth, a baby has about 350 bones; over the years, some of thesebones fuse into larger units. A baby’s skull is a good example ofthis. During birth, the skull is squeezed through a narrow canal. If the skull were as inflexible as an adult’s, it would be impossiblefor the baby to pass through the mother’s pelvic outlet. Thefontanelles, or gaps between the sections of the skull, allow theskull to be molded sufficiently to fit the birth canal. After birth,the baby’s fontanelles gradually close.

clavicle(collarbone)

sternum(breastbone)

humerus

radius

ulna

carpals

metacarpals

phalanges (digits)

patella (knee bone)

fibula

metatarsals

tibia

femur(thighbone)

coccyx

sacrum

pelvis (hip bone)

vertebral column (spine)

rib

scapula (shoulder blade)

cervical vertebrae(neck bones)

cranium (skull)

tarsals

phalanges

SEE ALSOelbow • feet • hip • joints • knee • leg • ligaments •muscle • shoulder • spinal column • tendon


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The skin is an organ—the largest the body has. It not onlyprotects the body from injury and infection but also keeps thebody’s temperature and moisture content stable. Through itsnetwork of sensory nerve endings, the skin picks up informationabout external stimuli for transmission to the brain. The skinenables people to feel things and to experience painful andpleasant sensations through touch.

The skin is also a good indicator of the body’s general health,because it is affected from within by the food eaten, by stresslevels, by hormonal balance, and by physical illness. A clear,glowing complexion is regarded as a sign of good health,whereas a pallid skin could suggest anemia and a yellow tone could indicate jaundice.

Structure of the skinThe skin consists of two parts: the epidermis and the dermis. The epidermis is the upper (outer) part of the skin. It has severallayers of cells, which are formed in the lower part, the dermis.Skin cells are constantly moving up to the surface, where they die and are formed into a material called keratin, which is finallyshed as tiny, barely visible scales. The dermis contains the sweatglands, sebaceous glands, apocrine glands, hair follicles, andnerves. The hairs and ducts from the glands pass through theepidermis to the surface. The apocrine glands are present in the armpits and other places and produce an odor.

Skin is categorized as oily, dry, or normal, but some people have combination skin, with both oily and dry patches, usually on the face. Oily skin is more prone to problems such as acneduring adolescence and early adulthood, but it ages better than dry skin, which wrinkles easily.

Skin color is due to the pigment melanin, which is produced in the lowest layer of the epidermis. The pigment-producing cells are larger in dark-skinned people than in fair-skinned people, but the number of these cells is the same. However, theamount of melanin produced varies, with dark-skinned peopleproducing more melanin than fair-skinned people. The pigment-producing cells are also responsible for freckles.

MolesMoles are dark spots made of collections of pigmented cells. They are very common and can be found anywhere on the body.Moles may be large or small, raised or flat, smooth or scaly, hairyor hairless. Most moles are present at birth or develop slowlyduring childhood. They may grow larger or darker in lateadolescence or when a woman is pregnant.

Skin

Q & AWhat factors affect how fastskin ages?

Inheritance is probably the mostimportant factor in skin aging.Other influences involved are the environment, such as theamount of sun damage, andhormonal changes throughoutlife. The loss of elasticity thatcauses wrinkles in old age is dueto changes in the fibers of thesupporting layer of skin. Skin alsobecomes drier and hair becomesthinner with age.

SHAVING

During puberty, which starts at any time from age 13 to age 15,boys begin to develop facial hair.The amount of hair that growsdepends on coloring and hormones.Blond men often have only a slightgrowth of hair, whereas those withdarker hair often have a thick,dense growth. Most men prefer toremove facial hair by daily shaving.

Women often shave the hairunder their arms, and those whohave noticeable hair on their legsmay shave them as well. To removeunwanted hair on other parts ofthe body, other methods of hairremoval are often more suitable.


181181

Most moles are harmless, but if a mole changes at all afteradolescence, particularly if it bleeds or itches, it must be shownto a doctor. New moles that appear on adults should also beexamined by a doctor. Sometimes, they may develop into a kindof skin cancer—malignant melanoma—and must be removed by surgery as soon as possible to prevent them from spreading.

Skin

nerve supply to hairfollicles, sweat glands,and skin receptors

cold receptor

sweat gland

arterial capillary

venous capillary

pressurereceptor

sebaceous gland

erector muscle

hair bulb

melanocyte

pain receptor

scales ofdead skin

pigmentgranules

heatreceptor

hair shaft

freckle

touchreceptor

EPIDERMIS

DERMIS

SUBCUTANEOUS FAT

The skin is made up of two differentlayers of tissues: the dermis and theepidermis. They sit above a layer ofsubcutaneous fat. Both the dermis andthe epidermis contain nerve endings, which transmit sensations, such as pain,pressure, heat, and cold. The sweat glandshelp regulate the body’s temperature, andthe sebaceous glands lubricate the skinand hair. The cells that produce pigmentdetermine skin color and produce freckles.

collagen andelastin fibers

SEE ALSOanemia • circulatory system • glands • nervous system •pain • skeletal system • skin • sweat


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Between two vertebrae of the spinal column is a disk of jellylikematerial, surrounded by a tough outer layer. The disk connectsthe vertebrae and acts as a cushion between them. Sometimeseveryday wear and tear or a sudden strain makes the tough outerlayer crack open. The inner layer bulges out and may press on anerve as it leaves the spinal cord. This condition is known as aslipped or prolapsed disk. It can cause severe backache. In somecases, any movement is very painful; even coughing or sneezingcan cause a sharp pain. The muscles along the spine may go intospasm or become weak or even paralyzed. The symptoms mayappear suddenly or they may build up over several weeks.

The most commonly affected disks are in the lower part of the back, where the greatest strains occur, but disks in any partof the back or neck can crack open.

Most people recover from a slipped disk simply by lying flat in bed. The soft inner disk material tends to dry and shrink once it has prolapsed, thus relieving the pressure on the nerve.Lying flat keeps the pressure within the disk to a minimum. In astanding position, this pressure is higher. It is best to put a boardunder a soft mattress—or even put the mattress on the floor—to prevent the back from bending. In severe cases, patients mayneed bed rest and pain relief for two weeks or more. Greatpatience is needed; getting up too soon often results in a relapse.

If the patient is free of pain, physical therapy can help. If thedisk is in the neck, the patient may need to wear a collar support.

Painkillers and musclerelaxants will ease the pain.

In a few cases, thedamaged disk may have to be removed by surgery. Patients areusually mobile againafter about two weeks.

Slipped Disk

Q & ADoes sleeping with a boardunder the mattress help preventa slipped disk?

No, sleeping with a board underthe mattress will not prevent a slipped disk. However, manypeople with back problems find that a firm mattress helpstheir back, because it is morecomfortable. A soft mattress can sag in the middle, so thatlying on the bed bends the back. This is an uncomfortableposition. Putting a hard boardunder a soft mattress is aninexpensive and effective way to increase comfort.

Are women more prone toslipped disks than men?

No. Two to three times as manymen as women suffer from aslipped disk. The reasons for this are not clear, and contrary to popular belief, heavy physicalwork is not associated with agreater risk of a slipped disk.However, a slipped disk isobviously more troublesome to someone who does heavymanual work than to someonewith a more sedentary lifestyle,such as an office worker.

SEE ALSObackache • muscle • pain • physical therapy • sciatica •spinal column • spinal cord

A slipped disk occurs whenthe soft inner core of aspinal disk bulges out andpresses on a nerve, causingmuscle weakness and pain.

lumbarvertebra

slippeddisk

spinalcord

disk


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The spinal column, or backbone, is the main bony support of the body. At the top, the spinal column supports the head. At the lower end, it is linked to the pelvis.

The spine consists of 33 small bones called vertebrae, whichare stacked on top of each other to form the spinal column. Thevertebrae are separated by disks with an outer fibrous ring andan inner pulpy center. These pulpy centers act as cushions andallow the spine to bend slightly. The spinal canal is a continuouschannel that holds and protects the nerves that form the spinalcord. The spinal cord is further protected by membranes and is surrounded by a liquid called cerebrospinal fluid, which acts as a shock absorber.

Of the 33 bones, 24 are movable. Seven bones form the neck and are known as the cervical vertebrae. Below them are 12 thoracic (chest) vertebrae and five lumbar (lower back)vertebrae. At the lower end are two groups of bones that arefused together to form two bones (the sacrum and the coccyx).

Spinal injuriesThe most common spinal injuries are a slipped disk (in which the pulpy content of the cartilage cushions moves out of place)and a fracture of the spine. A slipped disk is painful, but afracture of the spine may cause injury to the spinal cord and lead to paralysis. A patient with a suspected fracture of the spinemust be moved very carefully to avoid damaging the nerves.

Q & AIs the spinal column alwaysdamaged by a broken neck?

Not always. However, spinalcolumn damage often doesoccur when a person’s neck is broken. The spinal cord canalso be injured without thereever being a fracture of thespinal bones. This situation tends to happen when the cord is suddenly stretched ortwisted in an accident. Moreimportant than the fracture is whether any bones aredisplaced, causing them to press onto the cord in the spinal canal that runs throughthe spinal bones.

My grandmother, who is 63,recently told me that she is shrinking. She says she is 2 inches (5 cm) shorter now than she was 40 years ago. I believe her, but how can she possibly be shrinking?

As the body ages, the bones in the vertebral column getsmaller and the disks of cartilage between them get thinner and harder. Thismakes the disks shrink in size; with bone shrinkage, the person becomes shorter.

SEE ALSOfractures and dislocations • nervous system •paraplegia • slipped disk • spinal cord

Spinal Column

A cross section of part ofthe spinal column showsthe vertebrae separated by disks of cartilage. Thespinal cord lies within the spinal canal.

spinal cord vertebrae

intervertebraldisk

cerebrospinalfluid


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The spinal cord, running most of the length of the spinal column,is part of the nervous system. It provides a vital link between thebrain and the nerves connected to the rest of the body. There are31 pairs of spinal nerves, which branch out from the spinal cordto the surface of the body and the muscles.

The spinal cord makes the first analysis of sensations travelingto the brain and acts as a programming station for some basicmovements of the limbs. If a person touches something hot, for example, the message is processed before it reaches thebrain, producing an instant reflex action so that the hand pulls

away. Any further actionis dictated by the brain.Some automaticmovements, such as those involved inbreathing and digestion,are controlled partly bythe spinal cord.

Various diseases affectthe spinal cord, includingpoliomyelitis, multiplesclerosis, Lou Gehrig’sdisease (a type of motorneuron disease), andmeningitis.

The spinal cord canalso be damaged as a result of injuries to the spinal column.

Q & ACan ordinary viruses, such asthose that cause influenza, causean infection of the spinal cord?

This can occur, but it is rare.

Are the cells of the spinal cordlike brain cells, or are theydifferent?

The nerve cells, or neurons, of the spinal cord are the same as those of the brain. Althoughsome cells are specialized fortheir particular job ( just as some brain cells are), they are essentially the same.

Is the spinal cord alwaysseriously deformed when a baby is born with spina bifida?

No, the spinal cord is not alwaysdeformed. There are degrees ofseverity. It is only in the mostsevere type of spina bifida thatthe spinal cord is involved.

Spinal Cord

The spinal nerves controlsensations and movement in different areas of the body.If the spinal cord is damagedhigh in the neck, all of thelimbs will be paralyzed andthe patient will require helpto do many basic tasks, suchas eating and dressing.

brain spinal cord

31 pairs of spinalnervesbranchingfrom spinalcord

Body area controlled by cervicalspinal nervesBody area controlled by thoracicspinal nervesBody area controlled by lumbarspinal nervesBody area controlled by sacral spinal nerves

SEE ALSOmotor neuron disease • nervous system • paraplegia •reflexes • spinal column


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Healthy people need exercise, and one of the most enjoyableways of exercising is to take up some kind of sport. There are somany different sports activities that no matter where people liveor what sort of activity they prefer there is certain to be a sportthey can take part in and enjoy. Sports do not just keep the bodyfit and healthy; they are also an enjoyable way of meeting otherpeople and making friends.

Some people take their sports very seriously, spending a greatdeal of time, effort, and money on them. They may have to travela long distance to take part or to find the best surroundings andconditions. Others just want some fun and exercise. They willprobably look around locally and take up anything that seemsenjoyable and convenient.

Joining a teamMany people take part in sports in school or college. The choicesmay include team games such as baseball, football, and hockey.People who like these games often join clubs where they cancontinue playing after they finish school. Much of the fun ofteam games comes from interacting with other people, both

Q & ADo the warm-up exercises thatathletes do really prevent themfrom getting a stitch in the sidewhen they compete?

The purpose of an athlete’swarm-up is to ease muscles intowell-oiled working order withoutoverstraining them. Because astitch originates in thediaphragm, or in the musclesbetween the ribs, warming upshould help prevent it. However,when a stitch occurs because thebody is fatigued or sufferingfrom lack of salt, it is not likelythat warming up would havemade any significant difference.

My brother is a hemophiliac. He wants to play sports, but mymother thinks it would be toodangerous for him. Is she right,or should my brother be allowedto participate in sports?

He can enjoy an active life, butthere are certain restrictions. He must avoid contact sports,but he can still swim, run, andplay golf, for example.

Sports

Running in a relay requires a high level of fitness and skill. The runners need toundergo intensive training so that theycan achieve maximum performance.


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on and off the field. Clubs usually have nonplaying supporters as well, who get a great deal of enjoyment even if they do notget the benefit of exercise.

Many people do not enjoy team sports. They may enjoy gamesthat involve just a few players, such as racquetball or tennis.There are many clubs where these games are played and whichcater to all levels, from skilled players to absolute beginners.

Some people prefer track-and-field sports, in which theydevelop their own abilities as far as possible and then competeagainst others. Many places have athletic clubs where interestedpeople can get training in such sports. Here, sports are usuallytaken very seriously, and members spend a great deal of timeand effort in improving their fitness and skill.

Types of sportsNot all people are competitive—nor are all sports. Many peoplemeet to walk, run, hike, or bicycle together with no worries aboutwho is fastest or best. These sports have many advantages; they

Sports

Competitive cycling is an increasinglypopular sport in the United States.Whether people are cycling for sport or pleasure, they should always wear a protective helmet.

Mountaineering is an exhilarating butpotentially dangerous sport that hasclaimed many lives. It requires fitness andstamina, and only experienced climbersshould tackle difficult slopes. Youngmountaineers should always besupervised by an expert team leader, even on easy or gentle climbs.


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require no special training and littleequipment, and people can goalmost anywhere to carry them out.

Other sports depend on wherepeople live. Those who live near an ocean or lake shore can enjoy water sports, such as swimming,waterskiing, windsurfing, sailing,and sometimes surfing, rowing, or canoeing. Mountain dwellers can take part in climbing and skiing.Some sports such as horsebackriding are more common, less

expensive, and more enjoyable in the country than in a city. City people have the advantage of skating rinks and sportscenters and clubs. Sports are not just for the young. Althoughserious athletes peak in their twenties, many games allow olderpeople to make up in skill for what they have lost in speed andstrength. Sailing and golf are two examples of the sports thatcan be enjoyed by people who are no longer young in years.

Getting fitSome sports do people more good than others in terms offitness. Swimming rates highly; it improves the health of theheart and lungs and the suppleness of the joints, and it buildsmuscle power. All strenuous activities that make people puff and pant are good exercise for the heart and lungs, including ice skating, skiing, hockey, football, tennis, racquetball, rowing, brisk jogging, and cycling. Gymnastics and horseback riding areamong the sports that make the joints supple. However, no sportwill do much good unless people take part regularly and sensibly.

Warming upBefore starting any sports, people should do warm-up exercisesto prepare the muscles and avoid strains. It is best to wear theright clothes, including special shoes and protective headgearwhere necessary, and make sure that any equipment is safe and in good working order. Many sports, particularly the mostexciting ones, can be dangerous even for experts, and the bestway to avoid accidents is to learn from a professional teacher.

Sports

SEE ALSOexercise • heart • jogging • muscle • physical fitness •sports injuries • sprains and strains

This man is lifting his body using a metalbar. Whatever sports people take part in,they need to enjoy training to keep atpeak fitness levels.

Michael Phelps (b. 1985) set a new record for the most gold medals won at a singleOlympics when he won eight gold medalsin 2008. Swimming is one of the bestforms of exercise for overall fitness. It can be practiced as a competitive sport or simply enjoyed as a group, family, orsolitary activity.


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Almost every sport involves some risk of injury, from trivial cutsand bruises to more serious damage. Perhaps the most hazardoussports are those involving high speed (such as automobile racing,motorcycle racing, and skiing) and those carried out in dangerousplaces (such as mountaineering). Body contact sports (such asfootball and boxing) can also pose dangers. Some people are hurtaccidentally by equipment; for example, being spiked by a fellowathlete’s track shoes is a common injury.

Head injuriesHead injuries are a risk in contact sports such as boxing, whererepeated blows to the head can cause long-lasting damage asthe brain is knocked around inside the skull. Other sports arepotentially dangerous. They include football and wrestling, aswell as automobile, motorcycle, and bike racing. Horseback ridingis another sport in which serious head injuries, fractures, anddislocations can occur.

Potential brain damageAll head injuries are potentially serious, because they can causeskull fractures, concussion, contusion, or internal bleeding. If ahead injury is not correctly diagnosed and treated, headaches,loss of memory, and even permanent brain damage can result.However slight an injury seems, it is always best to get a doctor’s

opinion. A preventivemeasure, such as wearing a protectivehelmet, provides the best safeguard.

Muscle damage and tendon injuriesMost often, a sportsinjury follows the overuseof some part of the body.Muscle injuries are very

Q & AI wear dental braces. Can I use amouth protector to play football?

Anyone playing a sport thatcarries a risk of injury shouldwear a mouth protector. It willprovide a barrier between yourbraces and your cheek or lips,limiting the risk of soft tissueinjuries. Your dentist or yourorthodontist will help you select the most suitable mouth protector.

I recently took up golf. Should I be aware of any potentialinjuries?

Although some sports such as football produce far moreinjuries—and more seriousones—than golf, golfers cansuffer serious injury to theelbows, spine, knees, hips, orwrists. Golfer’s elbow is amongthe most common complaints,and strengthening forearmmuscles can help avoid this. The American Academy ofOrthopedic Surgeons suggestssome simple exercises, such as squeezing a tennis ball for five minutes at a time and doing wrist curls and reversewrist curls with a lightweightdumbbell.

Sports Injuries

This rock climber is using the proper safety equipmentand wearing a protectivehard hat. Young climbersshould always be supervised,and only experiencedclimbers should tackledifficult slopes.


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common and usually involve a rupture of some of the musclefibers. These injuries are described in various ways: as a pull, atear, or a strain. Soccer players frequently suffer injuries to thethigh muscles, calf muscles, and ankles; sprinters may damagethe hamstrings at the back of the thigh.

The Achilles tendon above the heel is commonly injured byrunners, hurdlers, and long jumpers; tendons (the fibrous cordsthat join muscle and bone) can also become inflamed throughoveruse. Rowers and racket players, for example, are at risk ofinflammation of the wrist and elbow tendons. Such injuriesshould never be taken lightly.

Torn ligaments and tendons require just as long to heal asfractures of the bones, and inflamed tendons may need severalweeks of rest from sports until the pain subsides. Even then, the return to sporting activity should be taken gradually to avoid further damage.

Knee and ankle injuriesKnee joints and ankle joints are particularly easy to injure, andonce they are damaged, they are prone to weakness later on.Apart from dislocation, one of the most frequent injuries to the knee is a torn cartilage, which is very painful and makesmovement of the knee difficult. Hairline fractures (shin splints)often occur in the shins of runners who overtrain on hard, jarringsurfaces, such as pavements.

Avoiding injuryMost sports injuries can be avoided through a mixture of fitnesstraining, adequate preparation for the particular sport, and

Sports Injuries

Soccer players often receive ankle injuriesas a result of careless tackling.

This girl fell down and hurt her kneewhile chasing after a ball.


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common sense. Conditioningexercises are very important,particularly at the beginning of the sports season, when fitnesslevels may not be up to standard.

If people are taking part in serious or competitive sports, they should be guided by theircoach, who will make sure that they have the appropriate trainingexercises before being allowed toplay. He or she will also insist onproper stretching and warm-uproutines before people undertakeany strenuous sports activity. If a

suitable warm-up is omitted or not properly carried out, manyinjuries can occur, such as strained elbows, damaged knee joints,pulled muscles, and stress fractures.

Treating sports injuriesWith most sports injuries, the first thing to do is to reduce thepain and swelling in the affected areas. A coach or a doctor canadvise on further treatment, which usually involves resting theinjured part for a few weeks or even longer. Sometimes physicaltherapy may be necessary.

Apart from minor injuries, all other sports injuries should beexamined by an expert. If there is any doubt, and particularly if pain is experienced, people with sports injuries should visit the emergency room.

Proceeding with cautionIf people have been out of action because of illness or injury, they must regain their fitness levels before they resume play. Too many people are tempted to make up for lost time by playing too vigorously and too soon after an injury has occurred.This action can lead to permanent damage or chronic weaknessin the injured part.

Sports Injuries

Weight lifting is an excellent activity forkeeping the muscles in shape. However, it is important to receive instruction firstto avoid causing unnecessary injuries.

Mountaineering is an exhilarating butpotentially dangerous sport that hasclaimed many lives.

SEE ALSOblack eye • bruises • fractures and dislocations •hamstring injuries • ice therapy • joints • knee •muscle • muscle diseases and disorders • physical

fitness • physical therapy • sports • sprains and

strains • tendon • tennis elbow


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Sprains are common injuries that happen to almost everyone atsome time. They are the result of twisting or wrenching a jointfarther than it can normally move. As a result, the ligaments thathold the joint in position are stretched and some of the fibers aretorn. The blood vessels in the area are usually torn, too. Strainsare less serious; fibers in the muscles are stretched or torn.

People often sprain an ankle if they trip or sprain a wrist as the result of a fall. Larger joints, such as the knee or hip, may be sprained during sports. A sprained neck can occur as a resultof whiplash injury in an automobile accident, although suchinjuries have become less common since safety belts and headrestrainers were introduced.

The obvious signs of a sprain are sudden, severe pain from the stretched or torn ligaments around the joint and swellingand bruising caused by bleeding in the area around it. This painbecomes much worse if the injured person tries to move or usethe joint or put weight on it.

Strained shoulder, leg, and wrist muscles and turned anklesare common sports injuries. The most frequent strains affect lessactive people and occur in the lower back as a result of pickingup a heavy or awkward object. Learning how to lift and carrythings properly can prevent back injury and pain. When liftingsomething heavy, it is best to keep the back straight and bendthe knees, letting them take the weight.

Rest, painkillers, and heat treatment will help most strains. Any injury more serious than a minor sprain should be examinedby a doctor, just in case a joint has been fractured.

Sprains and Strains

After first aid to help reduce the pain andswelling of a sprained wrist, a doctor willusually wrap the hand and wrist in anelasticized bandage to support the wristand prevent further injury.

Q & AWhat is the best type of bandageto use for treating a sprain?

The aim is to give the joint firmsupport while it heals, but itshould not be completelyimmobilized. Some form ofelasticized bandage is thereforerequired. An ordinary cottonbandage gives too little support,but crepe, webbing, and elasticbandages are all suitable. Thebandage must be tight enoughto be effective but not so tightthat it interferes with thecirculation; impairing thecirculation could causegangrene.

My friend recommended amassage to treat my sprain. Is that a good idea?

Perhaps. Gentle massage can be started when the immediateeffects of the injury have wornoff, usually on the second orthird day. The area will be verytender, so only light pressureshould be applied.

backache • exercise • fractures and dislocations • hip •ice therapy • jogging • knee • leg • ligaments • muscle •pain • shoulder • sports injuries

SEE ALSO


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When a person has a stroke, the normal blood supply to part of the brain is interrupted. A clot may form in one of the brain’sarteries and block it (cerebral thrombosis). A clot or piece ofartery wall from somewhere else in the body may be carried in the bloodstream to the brain and cause a blockage there(cerebral embolism). The most serious types of strokes are causedby an artery that bleeds into the brain (cerebral hemorrhage).

When the blood supply to part of the brain is cut off, that areaof the brain suddenly stops working. The patient’s symptoms willdepend on what functions this area controlled. A stroke maycause weakness or paralysis down one side of the body, loss ofsight on one side, or loss of speech or understanding. If a verylarge area of the brain is affected, the patient may die.

However, there are many cross-connections between neighboring

areas of the brain, so the area of damage is not usually verygreat. The brain has spare areas that, in time, may be

able to take over some of thework done by the damaged area.Thus, stroke patients may recover

almost completely after a while, withphysical therapy and speech therapy

when necessary.Strokes are caused by disease

of the arteries and high bloodpressure (which can weaken

the artery walls). Smokers and people with diabetes or a high level of cholesterol in the blood are at greater risk.

Q & AMy grandfather has just had astroke and can’t speak. Will hisspeech return?

Yes, it is very likely that his abilityto speak will come back, at leastto some extent. Sometimes,people are unable to speak at all in the first few days after astroke, but they later recoveralmost completely.

My uncle had a bad heart attackand then a few weeks later had a stroke that paralyzed his leftside. Was this connected with his heart attack?

After a heart attack, blood clotsmay form on the inside wall of the chamber of the heart.Occasionally, part of a clot candislodge and block off one of the brain’s blood vessels, thusproducing a stroke. Patients who have had very serious heart attacks can be givenanticoagulant drugs to helpprevent this.

Stroke

This stroke patient has aphasia. She hasdifficulty in understanding words as wellas speaking them. Here she attempts toname familiar objects. In time, and withgood therapy, she should recover her useof language skills.

blood pressure • cholesterol • circulatory system •diabetes • diet • dieting • exercise • heart attack •physical therapy

SEE ALSO


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Sugar is an important carbohydrate food. It supplies the bodywith energy, and its sweetness is used to enhance the taste of many foods and candies. All green plants make sugar. Thechemical name of sugar is sucrose. White sugar is the same as brown sugar except that it is simply more refined.

During digestion, sugars and starch are broken down intosimpler sugars called fructose and glucose. Other kinds of sugarsare lactose (present in milk) and maltose (present in corn). Thesesimple sugars are absorbed into the body and used as fuel toprovide energy for all metabolic processes. Some glucose isdiverted to the liver, converted to glycogen, and stored. Wheninstant energy is required, the liver converts some of the storedglycogen into glucose and releases it into the bloodstream. Ifthere is a temporary lack of carbohydrates, the liver is able tosynthesize glucose from fats and proteins.

All the cells in the body use sugar as a source of energy. Theblood contains about 0.1 percent glucose, which supplies energyto the various body tissues, especially to the brain.

Blood sugar, insulin, and diabetesHormones control the amount of sugar in the blood. The mostimportant of these hormones is insulin. Too little insulin, or atotal lack of it, leads to high concentrations of blood sugar. This

condition is calleddiabetes. Overproductionof insulin leads to toolittle sugar in the blood,producing a conditioncalled hypoglycemia,which quickly impairs the function of the brain.People suffering fromhypoglycemia learn torecognize the onset ofsymptoms and eat asugar-rich food to avertan attack.

Q & ADo glucose tablets and drinksprovide instant energy?

No. Glucose is the fuel that givesthe body energy, but it does notinstantly provide energy. Glucoseis stored in the liver and musclesas glycogen until it is required.The amount of glucose present in the blood is tiny, and more isadded from the glycogen storewhen blood sugar levels drop. All carbohydrates convert toglucose, so there is no need totake glucose tablets and drinks.

Why do diabetics have to restricttheir sugar intake?

A diabetic diet consists of acontrolled amount of allcarbohydrates. Diabetes iscaused by the inability of thebody to control the amount ofsugar in the blood, so the dietaims to provide the patient withthe exact amount of requiredcarbohydrates.

Sugars

Most sugar is produced using the juiceextracted from sugarcane. Brown sugar is generally less refined than white sugarand contains trace minerals and organicsubstances. Some brown sugars, however,are just white sugars that have beenartificially colored.

SEE ALSOappetite • basal metabolism • body systems • calories •carbohydrates • diabetes • diet • dieting • digestive

system • fats • food additives • food and nutrition •junk food • obesity • protein • weight control


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Sunburn is now less common than it used to be. People aregradually taking notice of doctors’ warnings that too much sun is a health risk. Sunburn is very uncomfortable, painful, anddangerous. Repeated sunburn can damage the skin permanently,and skin cancer is most likely to occur in fair-skinned people whohave spent a long time in strong sunlight.

Sunburn is caused by ultraviolet rays from the sun, whichdamage the outer layer of the skin. These rays stimulate the skinto produce a pigment called melanin, which darkens the skin to provide protection and acts as a filter for the ultraviolet rays.Sunburn occurs when there is not enough pigment produced by the cells to filter the sun’s rays.

Dangers of sunburnSunburn is not felt until a little while after it happens. The firstsigns are redness and a feeling of burning caused by an increaseof the blood supply to the skin. Sunburned legs and arms mayswell painfully, and the victim may develop a headache and feverand may vomit. Heat exhaustion may also occur. Blisters maydevelop, and the surface layer of skin may peel off.

Many people think that a suntan is attractive, but repeatedsun exposure over time makes the skin heavily wrinkled and

leathery. Patchy areas ofskin pigmentation andwartlike lumps (solarkeratoses) may develop.

Sunburn can be treatedwith soothing lotions andointments, but it is muchmore sensible not to getit in the first place. Whenout in the sun, peopleshould use sunscreenwith a high sun protectionfactor (SPF) to coverexposed areas of thebody. Otherwise, it is bestto keep out of the sun orkeep the skin covered.

Q & AI am fair-skinned and my friendis dark. Why can she spend along time in the sun withoutburning while I cannot?

Being fair-skinned means thatyou have little pigment in yourskin. Your friend has morepigment and can also makemore than you when exposed to sunlight. You will burn easily,because your skin cannot produceenough protective pigment, butit is dangerous for anyone tospend a long time in the sun.

My family is planning a vacationto the Caribbean. What can I doto reduce the risk of sunburn?

You could have a course ofultraviolet ray therapybeforehand, to increase yourpigmentation. You could also use a sunscreen preparation that filters out the sun’s strongerrays, allowing a slow tan todevelop. The best way to protectyourself is to stay out of the sun altogether.

Sunburn

A suntan does not prevent sunburn. Oncethe pigment-producing cells have beensaturated with ultraviolet light, furtherexposure causes burning, unattractivepeeling skin, and long-term skin damage.

SEE ALSOaging • blisters • circulatory system • heat sickness •pain • skin • sweat


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Perspiration, or sweat, plays a vitally important part in keepingthe body at the right temperature. A small amount of sweat isconstantly released onto the skin. As it evaporates, it cools downthe body. If people get hot, they perspire more heavily, and thisprocess cools them more quickly. If the body did not lose heat like this, people would suffer from heat stroke and die.

Sweat consists of water, salt, and, in some cases, organicmatter. There are two kinds of sweat glands, apocrine andeccrine. Apocrine glands are present only on the hairy areas ofthe body, such as the armpits and groin. Sweat from apocrineglands contains some of the cells from the gland linings, whereaseccrine gland sweat contains only water and salt. At puberty, theapocrine sweat glands develop. They produce increased underarmsweating and the odor that comes from sweat. A woman’s milk-producing mammary glands are a type of apocrine gland.

Most people produce about 1 pint (0.5 l) of sweat every day. In very hot conditions, people may produce a lot more, and theyneed to drink a lot of water and take salt tablets to replace whathas been lost. When people have a fever, the body temperaturerises, and they perspire noticeably. Episodes of perspiring,particularly at night, can be a symptom of some types of

illnesses. Anyone with a fever should drink plenty of fluids.

The organic matter in sweat is broken downby bacteria on the skin surface to produce anunpleasant smell,particularly under thearmpits. This body odorcan be controlled byshowering daily and by wearing clean clothesevery day. Deodorants just mask the odor;antiperspirants reducepore size or clog the poresto retard perspiration.

Q & AIs perspiration just another wordfor sweat?

Yes, but perspiration generallydescribes moderate sweating—asteady production of sweat thatdoes not form into heavy droplets.

Why do some people seem tosweat more than others?

The mechanism of sweating iscontrolled by the nerves and is affected by both a person’sexcitability and the state of theskin’s blood vessels. Heavierpeople have to sweat more tocool themselves off, and anxiouspeople sweat more because theirnerves are more active.

Is there anything I can do to stop my feet from sweating?

The short answer is no. The solesof your feet, like the palms ofyour hands, have many hundredsof sweat glands that areimportant for controlling yourbody temperature.

Sweat

Frequent showering or bathing helpsprevent perspiration from causing bodyodor. In hot weather, a lukewarm shower helps to keep the body cool and isextremely refreshing.

SEE ALSOdrinking water • glands • heat sickness • nervous

system • salt • skin


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muscle fiber muscles tendonsheaths

tendon

tendons

A tendon, also called a sinew, is a very tough band of fibroustissue that connects a muscle to a part of the body, usually abone, so that it can carry out movements. Tendons are extensionsof muscles; their fibers fuse with the connective tissue thatcovers the bone.

Several tendons are located close to the surface of the bodyand can be easily felt. An example is the hamstring tendon at theback of the knee. Others can be seen in the backs of the handsand the soles of the feet. Tendons run inside sheaths at thepoints where they cross or are in contact with other structures.Each sheath is a double-walled sleeve, with the space betweenthe walls filled with lubricating fluid. Repeated movements maycause the fluid to run dry. Rest is essential until this fluid buildsup again; otherwise inflammation, called tendonitis, may result.

Q & AMy boyfriend accidentally cutone of the tendons in his wrist.Will he be able to use his handafter the tendon has healed?

In most cases, it is possible tosew the cut ends of the tendontogether again. This is usuallysuccessful in restoring fullmovement to the affectedmuscle on recovery. However, the tendon may not be as strongas it was, and its use may giverise to discomfort.

Can tendons be dislocated?

This is an unusual occurrence,but it can happen. Normally it is brought about by a suddenwrenching movement, powerfulenough to jolt a tendon out ofthe groove over a bone in whichit runs. Treatment consists ofmanipulating the tendon backinto its proper position.

Tendon

The muscle fibers merge to form tendonsthat are attached to bones. Where thetendons cross each other or otherstructures, they are protected by a fluid-filled sheath.

Achilles tendon

muscle • muscle diseases and disorders • sports injuries

SEE ALSO


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Tennis elbow is inflammation of the tendon where it attaches to the bone at the outer side of the elbow. The tendon links themuscle in the upper arm to the bone in the forearm and canbecome damaged owing to repeated use of the forearm, such asplaying backhand shots in tennis. Other types of activities, suchas excessive use of a screwdriver (where the wrist and forearmare vigorously worked), can also cause tennis elbow. The tendonbecomes pulled, and small tears may occur, leading to pain andtenderness in the area.

Symptoms and treatmentsWhen someone suffers from tennis elbow, the elbow looksnormal, and bending and straightening the arm are painless and unrestricted. However, there is fairly constant pain andtenderness experienced in the elbow region. In severe cases, the pain may be felt over a much wider area, often extendingwell over the back of the forearm. The pain is made worse byactions such as turning a stiff doorknob or unscrewing a jar top.

Most cases of tennis elbow settle with physical therapy, icepacks, exercises to stretch and strengthen the affected muscles,

ultrasound treatment,and the avoidance of any activity thatcauses pain. Somepeople have foundacupuncture and heattreatment helpful.

If these actions fail, a doctor mayinject a corticosteroidwith a local anestheticinto the affected area.In rare cases, surgerymay be needed. If thecondition is caused by playing sports,expert coaching ontechnique may benecessary.

Tennis Elbow

Q & AIf I had tennis elbow, how wouldI be able to recognize it?

You would have a dull achearound the elbow area andupper side of the forearm, with a particularly tender spot on the bump that can be felt on theupper side of the elbow whenthe forearm is placed across thechest. Typing, using a squash ortennis racket, or even picking upheavy objects may be painful.

How soon can one resumeplaying tennis after tennis elbow?

That depends on how serious theinjury was; you should seek yourdoctor’s advice. The symptomsvary from person to person. Inmild cases, it may take only a few days until the pain andstiffness subside, and then youcan resume the sport gradually.More serious cases may takelonger. If the tenderness returnswhenever you play, consult yourdoctor as soon as possible.

Serena Williams follows through after abackhand shot. Tennis players can sufferfrom tennis elbow, usually as a result of overuse of the muscles and tendonsused to hit a backhand shot.

SEE ALSOacupuncture • elbow • ice therapy • muscle • pain •physical therapy • sports injuries • tendon


198

Most people feel tired after a day’s hard work or exercise. Theymay also feel tired during the day if they have slept badly theprevious night. Usually, a good night’s sleep is all that is neededto make the tiredness disappear. However, tiredness can also be a sign of illness. A person with persistent tiredness may havedaytime sleepiness and a lack of energy, loss of motivation, poor concentration, difficulty in making decisions, anddepression.

Often, tiredness is due to a combination of causes. Nine in 100 people with tiredness have a physical disease; about 75 in100 people have an emotional condition. The most commoncause of abnormal tiredness is an infection.

Sometimes, tiredness is an early warning of an illness; peopleoften feel tired for a day or two before developing influenza orthe common cold. Tiredness is also the main symptom of somemild infectious diseases, such as rubella (German measles) andinfectious mononucleosis. Diseases such as measles, chicken pox, and influenza often leave people feeling tired and run down.

Two other common causes of tiredness are anemia andhormone diseases (including lack of thyroid hormone anddiabetes). However, tiredness can also have mental or emotionalcauses, including boredom, anxiety, and depression. Severe, long-term, debilitating tiredness may be a symptom of chronic fatiguesyndrome. This condition does not readily respond to treatment,but many sufferers find they improve over time.

Tiredness, fatigue, and lethargyTiredness is alsosometimes known asfatigue (weariness orexhaustion caused byexertion). Lethargy,however, usually meansan indifference to events,a general lack ofinclination to take part in any activity, or anabnormal lack of energy.

Q & AHow can you tell the differencebetween a person who is lazyand a person who is tiredbecause of an illness?

In general, the lazy person is ableto find a huge amount of energyto do what he or she enjoysdoing, whereas a truly exhaustedperson cannot summon upenthusiasm for anything.

My grandmother, who is 81,seems very feeble and tiredlately. She thinks this conditionis due to her age and won’tconsult her doctor. Is she right?

Although there is some loss ofenergy in old age, it should beslight and gradual. Anythingmore should not be accepted asnormal or inevitable and shouldbe investigated, because it canoften be helped. Anemia andinadequate nutrition may be dueto a reluctance to buy and cooknutritious food; this problem iscommon in older people. Yourfamily should continue trying topersuade your grandmother tosee a doctor about her tiredness.

Tiredness

Babies cry when they are tired. They mayalso become so overtired that they areunable to sleep and need to be calmed.

SEE ALSOanemia • chronic fatigue syndrome • diabetes • exercise

• lethargy • rest and relaxation


199

Vegetarians are people who do not eat meat. They may dislikethe idea of animals being killed to provide meat, find the taste ofmeat unpleasant, or feel healthier on a vegetarian diet. Doctorsmay suggest a vegetarian diet for certain medical conditions.Some religions and spiritual sects forbid eating meat, and certainIndian and African communities eat no meat.

Many vegetarians do eat dairy products, such as milk and eggs.People following a macrobiotic diet eat foods based on wholegrains, cereals, some vegetables, and occasionally fish. Vegans eat no animal products of any kind. People considering avegetarian diet should take a responsible approach to ensurethat they have a regular intake of essential vitamins andminerals, because strict vegetarians can lack some of theseessential substances in their diet.

A properly balanced vegetarian diet can contain all thenutrition people need to keep healthy. It also has the advantageof being low in saturated fats (which can cause heart disease)and high in fiber. Eggs and cheese provide protein, but veganscan also get enough protein by combining cereals, nuts, legumes,potatoes, and oil seeds. Some vitamins (including vitamin B andvitamin D) are not present in plants, so vegans should takevitamin supplements to provide them.

SEE ALSOdiet • digestive system • food and nutrition • minerals •nutritional diseases • protein • vitamins

Vegetarianism

In terms of land use, it is moreeconomical to grow crops than to grazeanimals for slaughter. If less grain wereused to raise animals, more would beavailable for humans to eat. About 50percent of the world cereal crop is fed to animals, and it takes 10 tons ofvegetable protein to yield just one ton of animal protein.

61 people

SOYBEANS WHEAT MAIZE MEAT

24 people 10 people 2 people

10 acres (4 hectares) of land feed the following number of people:


200

To function efficiently, the body needs vitamins. These chemicalsubstances are involved in the processes of repair andmaintenance of the body’s tissues. Some vitamins are made by the body—for example, the skin can make vitamin D fromsunlight—but people get most of the vitamins they require fromfood. A balanced diet should provide all the essential vitamins.

Many nutritional diseases are caused by lack of vitamins in the diet. All the B vitamins are necessary for the proper operationof various enzymes. Vitamin C is required for the production of healthy collagen (the structural protein present in bones,ligaments, and tendons). Vitamin C is also a powerful antioxidantthat mops up damaging chemical groups called free radicals.

Naming vitaminsVitamins are generally known by letters of the alphabet, andsometimes by other names. The main vitamins are A, B, C, D, E,and K. Of these, A, D, E, and K are fat-soluble and can be stored in the body, but vitamins B and C are water-soluble and cannot.

Deficiency diseasesMost people in developed countries get all the vitamins theyneed in their everyday food. The exceptions are elderly people,alcoholics, and those who cannot afford appropriate food. Somepeople have deficiency diseases because their bodies cannotabsorb the vitamins they eat. Deficiency diseases still occur inpoor parts of the world where the diet is inadequate or wherefood is scarce. Perhaps the most common vitamin deficiency is vitamin A (which causes eye problems). The body can makevitamin A from fresh vegetables but they are in short supply in developing countries. Hundreds of thousands of children goblind every year from vitamin A deficiency. Their corneas soften,melt, and split, and infection destroys their eyes.

Many people throughout the developed world take vitaminsupplements in the belief that vitamins will keep them healthy,although everyone who eats a properly balanced diet shouldhave sufficient vitamins from the food that is eaten. Indeed, extra intake of certain vitamins can be harmful. However,vitamins C and E are known to protect the body against freeradicals, which are thought to be implicated in many diseasesand are involved in the deposition of harmful cholesterol in theartery walls. Numerous clinical trials have shown that peoplewho have an above-average intake of the antioxidant vitamins C and E also have a lower-than-average incidence of thesediseases. For these reasons, millions of people now take dailyvitamin supplements.

Q & AWhat are vitamins and howimportant are they?

Vitamins are organic substancespresent in minute amounts infood. They help make the bodywork. Because they cannot bemade in the body, vitamins must be obtained from the dietor from sunshine. A personrequires only small amounts, but vitamins are neverthelessessential to normal metabolism.

I have very low energy levels.Have I got a vitamin deficiency?

It is most unlikely that a personon a normal diet would suffer avitamin deficiency. The only timeextra vitamins should be taken is when you are on an abnormalor restricted diet.

Can taking too many vitamins be harmful?

Taking too much vitamin A andD can be harmful. Too muchvitamin A can result in fragilebones, enlargement of the liverand spleen, and loss of appetite.Vitamin D overdose can causevomiting, headache, weight loss,and calcium deposits in thekidneys and arteries.

Vitamins


201

Vitamins

VITAMINS AND VITAMIN DEFICIENCYVitamin Deficiency symptoms Good sources

A (retinol)

B1 (thiamine)

B2 (riboflavin)

B3 (niacin; alsoknown as PP,which stands for pellagra-preventing)

B5 (pantothenicacid)

B6 (pyridoxine)

B9 (folic acid)

B12(cyanocobalamin)

C (ascorbic acid)

D (calciferol)

E (tocopherol)

K (phylloquinone)

Night blindness, growthretardation, aggravation oflung diseases, rough dryskin, and blindness

Memory loss, appetite loss,digestive disturbances,fatigue, nervousness, andberiberi

Corner-of-mouth cracksand sores, dizziness, lightsensitivity, and eye lesions

Appetite loss, headaches,depression, memoryimpairment, nervousdisorders, and pellagra withsymptoms of dark, scaly skin

Very rare

Low levels sometimesfound in women who arepregnant or on the Pill;associated with fatigueand depression, irritationof the lips, and dry skin

Digestive disturbance,growth problems, anemia,and possibly spina bifida

Fatigue, memoryimpairment, perniciousanemia, and degenerationof nerve cells

Anemia, bleeding gums,and scurvy

Bone deformity (ricketsand osteomalacia) andpoor teeth

Hemolytic anemia inpremature infants

Impairment of blood-clotting process

Liver, fish, dairy products,eggs, carrots, greenvegetables (particularlyspinach), and margarine

Whole-grain cereals,fortified breakfast cereals,meat, milk, greenvegetables, brewer’s yeast,wheat germ, and yeastextract

Milk, organ meats(particularly liver), eggs,and green vegetables

Lean meat, liver, legumes,fortified breakfast cereals,bread, eggs, and milkproducts

Most foods

Most foods (particularlymeat, vegetables, yeast,cereals, bread, milkproducts, and eggs)

Most green leafyvegetables, organ meats,legumes, and bread

Dairy and animal products(particularly liver)

Fresh fruits (particularlycitrus and black currants),vegetables, and potatoes

Cod liver oil, egg yolk, fattyfish, butter and fortifiedmargarine; also made bythe body in sunlight

Most foods, especiallycereals, eggs, nuts, wheatgerm, and vegetable oils

Dark green vegetables and liver; also made bybacteria in the intestine

LIMEYS

Vitamins were discovered in the early twentieth century, buthundreds of years ago peoplerealized that eating certain foodshelped keep them healthy, even if they did not know why. In 1753, a British naval surgeon describedhow lemons, limes, and other citrus fruits could prevent sailors at sea from getting a disease called scurvy, which caused spongygums, loose teeth, and bleedinginto the skin. This is why Britishsailors came to be nicknamed“limeys.” Now people know thatscurvy is caused by a lack ofvitamin C, which is present in fresh vegetables and especially in citrus fruits.

Junk food may be very tasty, but it isdeficient in essential nutrients, especiallyvitamins. For this reason, it should notform a major part of the daily diet.


202

Vitamin AVitamin A is present in liver, fish oils, dairy products, and eggyolks. The body can also makevitamin A from the substancecarotene, which is present incarrots and green vegetables. Vitamin A plays a part in boneand tooth formation, inmaintaining the membranesthat line the body tubes, ingeneral growth, and in keepingthe tissues of the eyes healthy.Vitamin A can be stored in theliver. A deficiency of Vitamin Amay cause night blindness, poor skin, and poor bone growth.

A balanced diet, rich in fresh fruitsand vegetables, provides all thevitamins the body needs to stayhealthy.

Vitamin B complexThe vitamin B complex is a groupof vitamins. Vitamin B1 is alsocalled thiamine. It is needed to keep the brain, nerves, andmuscles working. Vitamin B2,(riboflavin), vitamin B3 (niacin),and vitamin B6 help the bodybreak down food for energy, andvitamins B9 (folic acid) and B12(cyanocobalamin) are essentialfor making red blood cells. The B vitamins are present in liverand meat, and some are presentin nuts and vegetables. The body cannot store B vitamins, so people need to eat themregularly. Lack of B vitaminscauses disorders of the heartand nervous system and diseases such as pellagra, anemia, and beriberi.

Vitamin CVitamin C is an antioxidant with many valuable properties. It plays an important part ingrowth and healing andstrengthens the immunesystem. It is present in fruits(especially citrus fruits) andvegetables. Vitamin C cannot bestored in the body, so if peopleeat more than they need, theexcess is excreted in the urine.For this reason, it is important to eat vitamin C–rich foods dailyto restore the body’s supplies.

Vitamins

Vitamin A Vitamin B

Vitamin C


203

Vitamins

Vitamin DVitamin D helps people absorbcalcium and phosphorus andbuild up a healthy bonestructure. It is especiallyimportant for babies and youngchildren, because their bodies are growing very fast. The bodycan make vitamin D fromsunlight, but it is also present in oily fish, eggs, and dairyproducts. People with fair skinmake more vitamin D than those with dark skin. Withoutvitamin D, children suffer fromrickets (bone deformities as aresult of inadequate supplies of calcium and phosphorus) and poor teeth.

Vitamin ELike vitamin C, vitamin E is apowerful antioxidant. It is fat-soluble and functions in thefatty cell membranes to helpprotect them against freeradicals. It is present in mostfoods, particularly vegetable oils,whole-grain cereals, dark greenvegetables, and wheat germ.Deficiency can cause muscularproblems and may also lead to fertility problems.

Vitamin KVitamin K plays an importantpart in the clotting of blood.Dark green vegetables, potatoes,wheat germ, cheese, liver, andeggs are good sources. Vitamin K can be made by the action of bacteria in the intestines.Although most people getenough vitamin K, deficiencymay occur in those people withliver disorders, malabsorption,and chronic diarrhea.

Vitamin D

Vitamin E

Vitamin D

Vitamin K

SEE ALSOanemia • diet • dieting • food and nutrition • health foods

• malnutrition • minerals • nutritional diseases • scurvy


204

Measuring a patient’s weight is a standard part of any medicalexamination, because weight is often a clue to someone’sgeneral state of health. People who are overweight put an extra strain on their body, in particular on their heart. They need to lose weight to maintain their health.

Weight can be lost by dieting sensibly—eating no more than the body needs, while ensuring that it gets essentialnourishment—and increasing exercise levels.

Compulsive overeatingNow recognized as an illness, compulsive overeating is a majorcause of obesity, together with emotional unhappiness. Manypeople are secret food addicts who overeat to cover up theiranxieties. For them, food offers comfort and security. It is mostlywomen who are driven to compulsive overeating, often in bingesthat are followed by drastic purges. Although the risks to mentaland physical health are considerable, such people are oftenunable to help themselves. Psychotherapy or organizations suchas Overeaters Anonymous can help find the underlying causes ofthe compulsion and help people to control their weight sensibly.

Dangers of being underweightBeing underweight can also be unhealthy. It makes people easily tired and less resistant to infection, and it is often a sign that

something is wrong. Some peoplelose weight when they are worriedor upset, but loss of weight can alsobe one of the first signs of illness.People who find that they are morethan a few pounds underweight or who are losing weight for noobvious reason should see a doctor.Tests can show if there is anunderlying problem, and treatmentcan be started immediately.

Q & AI want to lose weight, andseveral of my friends havesuggested that I should jointheir yoga class. Can I really lose weight by taking up yoga exercise?

Yoga alone may not cause you to shed many pounds, but youshould look and feel more trim,because yoga exercises firm andtone the muscles. Yoga posturesfirm up the abdomen, upperarms, and thighs, which areprone to flabbiness if you aredieting.

Should I use diet pills to try to lose weight?

Doctors agree that the best wayto lose weight is to eat less andexercise regularly.

I am overweight, and nothingI’ve tried in order to lose theweight has worked. Could I have a problem with my adrenal glands?

If your excess weight isdistributed evenly, the answer is no. There is only one disease of the adrenals (Cushing’ssyndrome) that gives rise toobesity and it is extremely rare.

SEE ALSOanorexia and bulimia • diet • dieting • exercise • food

and nutrition • obesity • physical fitness • yoga

Weight Control

Many obese children find reducing weightenjoying and rewarding. Taking part insports makes them fitter and increasestheir self-esteem.


205

Yoga is a series of exercises or postures that relax the mind andthe body and emphasize harmonious coordination of movement,stretching, and breathing. Yoga also helps tone muscles andstimulate blood circulation.

The exercises are intended to work on the whole body. Theyare performed slowly, gracefully, and thoughtfully. Each posture is held for a period of time to give the muscles a chance to derivethe maximum benefit from the position.

Special breathing techniques are used in conjunction with yoga exercises. The basis of yoga breathing is a deeply indrawnbreath through the nose, which first expands the abdomen, then the rib cage, and then the chest.

Yoga is an ideal exercise for people of all ages. Because thereare no quick or jerky movements, it is suitable for young children

and elderly men and women.Yoga is also good for teenagers

and younger people, becauseit helps develop grace,poise, and concentration. Mental tranquillity is

another benefit of yoga.Most people say

that they feel bothrefreshed and

relaxed after a session of yoga. Although

it requires practice to master the

exercises, evenbeginners soonexperiencefeelings of

well-beingafter acouple

of yogasessions.

Q & AI feel tense all the time. Couldyoga help me relax?

Yoga is aimed at relaxing boththe body and the mind. Theasanas, or postures, are alsoperformed slowly and gracefully,so the mind is soothed while the body is exercised. Breathingexercises and relaxation posturesare good for relieving tension.

I’m sure I can’t do the difficultpostures I see in yoga books. Is that what yoga’s about?

No. You have seen postures foradvanced students. There is a wide range of simple andgraceful exercises for beginners.However, with practice, you willeventually be able to get intopostures that you once thoughtwere completely impossible.

My eight-year-old sister wants totake up yoga. Is she too young?

No. Her youthful flexibility willgive her a great advantage. The exercises will teach her body control, concentration,gracefulness, and the ability torelax. She will probably progressfast and soon be able to mastercomplicated postures.

Yoga

The lotus position is probably the best-known yoga pose. This meditationposture helps createserenity of mind and a feeling of well-being.

aerobics • alexander technique • circulatory system •exercise • isometric exercises • muscle • physical

fitness • rest and relaxation

SEE ALSO


Index

206

Page numbers in boldtype refer to main entries;italic type refers toillustrations or captions.

Aacetaminophen 12, 152acetylcholine 23Achilles tendon 126, 196achondroplasia 100acne 165, 180acquired

immunodeficiencysyndrome (AIDS) 27,128

acupressure 5acupuncture 6, 150, 152adolescence 164adrenal glands 40, 41, 77,

96, 97, 103, 164, 204adrenaline 11, 77, 96aerobics 7, 73, 105, 118,

156–157, 159aging 8–9, 18, 121, 131–132,

180, 198AIDS see acquired

immunodeficiencysyndrome

alcohol 13, 27, 66, 81, 112,129

aldosterone 96Alexander technique 10,

162alimentary canal 63allergic reactions 23–24,

90, 115–116alveoli 39, 168, 169amino acids 134, 163aminophylline 24amphetamine 11amputation 141, 152amylase 63amyotrophic lateral

sclerosis 136anabolic 32anabolism 32analgesics 12, 152anemia 13–14, 51, 66, 76,

114, 149, 202hemolytic 14pernicious 13–14sickle-cell 14

angina 105ankle 38, 111, 126, 189ankylosing spondylitis 21ankylosis 120anorexia nervosa 15–17,

129antibodies 38, 39, 96, 131antioxidants 18, 81, 176,

200, 202, 203anus 40, 52–53, 64, 65aorta 50, 50, 103apathy 128–129aphasia 192apocrine glands 180, 195appendicitis 66

appendix 65, 66appetite 19arteries 35, 37, 48, 50, 50,

75, 103, 145, 200atherosclerosis 48, 81,

105coronary artery disease

103, 105arterioles 37, 50arthritis 20–22artificial limbs 70, 70asbestos 71aspirin 12, 20, 21, 152asthma 10, 23–24, 27, 47,

149, 158atherosclerosis 48, 81, 105athlete’s foot 25, 79, 161attention deficit disorder

11autonomic nervous

system 26–27, 141, 142axons 26, 141

Bbackache 28–29, 182

Alexander technique 10sciatica 174

backbone see spinalcolumn

bad breath 67balance 30–31, 41basal metabolism 32, 58belching 66beriberi 144, 202biceps 72bile 63biofeedback 152bioflavonoids 81bionic body parts 70black eye 33bladder 27, 40, 137bleeding 111blinking 167, 167blisters 34blood 37, 38, 50, 163

anemia 13–14bruises 33, 42cholesterol 48, 61, 134,

192lymphocytes 96, 97oxygen 103, 114,

168–169sugar 55–57, 76, 96, 109vessels see arteries;

capillaries; veinswhite cells 38, 39see also circulatory

system; heartblood pressure 35, 154, 173body clock 97body odor 96, 180, 194body systems 36–41bones 37, 38, 43, 98, 123,

134, 163, 178–179, 196,202, 203

aging 8dislocation 93–95

fracture 93–95,146–147, 146, 147

grafts 126, 147orthopedics 146–147ossification 178see also joints; skeletal

systemborborygmi 115botulism 66, 92brain 26, 27, 31, 36, 40–41,

41, 141, 142, 151, 155oxygen supply 149

brain stem 151breast-feeding 63breathing 26, 39, 39, 141,

168, 169, 184, 205bronchi 23, 27, 39, 168, 169bronchioles 39, 168, 169bronchitis 24, 149bronchodilator 23bruises 42, 111, 191

black eye 33bulimia 15–17bunions 79, 147, 161, 161burns 34bursa 72, 125bursitis 72, 119

Ccaffeine 51, 112calcaneus 78, 78calcium 43, 58, 87–88, 96,

110, 134, 135, 203calluses 80calories 44, 60, 86, 91cancer 13, 18, 68, 71, 81, 102,

124, 181capillaries 37, 42, 50, 64,

103, 168–169carbohydrates 44, 45, 63,

85–86sugars 45, 193

carbon dioxide 37, 38–39,50, 103, 110, 168–169

carotenoids 18cartilage 37, 98, 121, 123,

125, 178ossification 178osteoarthritis 20, 21torn 123

casein 63catabolism 32celiac disease 46central nervous system

(CNS) 40–41, 41, 141cerebellum 27, 31cerebral cortex 151cerebral embolism 192cerebral hemorrhage 192cerebral thrombosis 192cerebrospinal fluid 183chi 5chicken pox 34, 198chilblains 78–80, 80Chinese healing

techniques 5–6chiropractic 29, 47

chlorinated water 71chocolate 81, 89cholera 66cholesterol 48, 61, 77, 81,

85, 105, 134, 192, 200chromium 135chronic fatigue syndrome

49, 129, 198chyme 63, 64, 65circulatory system 37, 38,

50, 103, 168clavicle 29, 177clubfoot 79, 147, 161coccyx 28, 29, 183cocoa 51codeine 12, 152coffee 51cold, common 24, 198cold sores 34colitis 52, 66collagen 130, 163, 178, 200colon 64, 65, 66, 68, 116compulsive overeating

204connective tissues 36constipation 47, 51, 52–53,

66, 68, 115copper 58, 135corns 79, 80, 80, 161coronary arteries 105coronary artery disease

103, 105coronary thrombosis 35cortisol 96cortisone 21cramps 54, 139–140, 173

heat 106Crohn’s disease 66Crosby capsule 46Cushing’s syndrome 204cyanosis 149

Ddehydration 71, 106dendrites 141deoxyribonucleic acid

(DNA) 36depression 9, 10, 11, 73, 129,

155, 171, 198dermis 180, 181diabetes 27, 51, 55–57, 62,

73, 75, 105, 145, 192,193, 198

type 1 (insulin-dependent) 55

type 2 (noninsulin-dependent) 56

diaphragm 168diarrhea 66, 68, 71, 92, 115

spurious 66diastolic pressure 35, 35diet 58–59, 155, 157

antioxidants 18, 81bread 102calories 44, 60, 86, 91carbohydrates 44, 45,

63, 85–86, 193

cholesterol 48, 61, 77, 81,85, 134

coffee 51digestive system

disorders 66eating disorders 15–17fats 44, 45, 46, 48,

58–59, 60–61, 63, 66,77, 85–90, 102, 124

fiber 58, 62, 66, 87–88,112

flavonoids 18, 81food additives 82–83,

90, 91, 102, 124food labeling 91growth 99health foods 102indigestion 112junk food 124macrobiotic 58, 199malnutrition 131–132minerals 144nutrition 84–90nutritional diseases

144proteins 44, 45, 58,

60–61, 63, 85–86, 88,102, 131, 134, 163

salt 60, 61, 89, 173scurvy 176sugars 45, 60, 63,

89–90, 124, 193tea 51vegan 199vegetarian 58, 84,

199vitamins 85–88, 132,

144, 176, 200–203weight control 60–62,

204see also food; minerals;

vitaminsdieting 11, 15–17, 60–62,

204basal metabolism 32

digestive system 26, 37,39–40, 40, 41, 45,63–65, 137, 184

autonomic nervoussystem 26, 27

diseases and disorders66–68

indigestion 112malabsorption 67

disabilities 69–70dislocations 93–95, 119diuretic 51diverticular disease 68diverticulitis 52–53dizziness 27, 31, 35drinking water 71, 85–86drugs

amphetamines 11analgesics 12, 152drug abuse 129ecstasy 11narcotics 152

NF_MC Bind_UP_pp206-208_Index.qxd:Nutrition And Fitness 4/19/10 4:23 PM Page 206

207

nonsteroidal anti-inflammatory drugs(NSAIDs) 12, 12

duodenum 63, 65, 66dwarfism 100, 147dysentery 66, 92dyspepsia 66

Eear 30, 30, 41eardrums 30earwax 97eating disorders 15–17eccrine glands 195elastin 130, 178 elbow 72, 120, 123, 130, 197electrocardiogram (ECG)

105embolism 122, 192emphysema 149endorphins 5, 152enzymes 63–65, 163, 200epidermis 180, 181epiglottis 168epilepsy 76epithelial tissues 36, 36,

37, 37esophagus 39, 63, 65eustachian tube 30exercise 8–9, 44, 73–75,

155–159, 170, 185–187aerobic 7, 73, 105, 118,

156–157, 159anaerobic 73countering depression

9isometric 117, 157jogging 118, 156sports 185–187yoga 74, 205

eyes 41, 97black eye 33

Ffainting 27, 76, 150fallen arches 78fat cells 37fatigue see tirednessfats 58, 60, 63, 77, 85–90

saturated 48, 61, 77, 85,102, 105, 124, 199

unsaturated 48, 77, 102fatty acids 63–64, 77feces 40, 58, 64feet 78–80, 123, 147

athlete’s foot 25, 79, 161podiatry 161shoes 28, 34, 78–80sweating 195

femur 29, 108, 108, 123,125, 125, 126, 127

fertilization 41fetus 98, 98fever 12fibromyalgia 29fibula 126, 127finger joints 123flat feet 78, 147, 161flatulence 66, 115flavonoids 18, 81fluid retention 173fluoride (fluorine) 58, 135folic acid 13, 51, 202fontanelles 179

food 71, 84–90allergies 115–116cooking methods 89,

92health foods 102hygiene 172junk food 90, 124labeling 82, 91malnutrition 131–132processed foods

89–90, 102pyramids 59, 59, 87–88see also diet; nutrition

food additives 82–83, 90,91, 102, 124

food poisoning 66, 92salmonella 66, 92, 172

fractures 93–95, 146–147,146, 147

compound 93, 94depressed 93greenstick 93, 94, 178pathological 93simple 93

freckles 180, 181free radicals 18, 200, 203fungal infections 25, 79,

161funny bone 36, 72

Ggallbladder 63–64, 65gallstones 145gastric juices 39, 40, 63gastritis 67gastroenteritis 67genes 36genetic code 163gigantism 100glands 77, 96–97, 141

apocrine 180, 195endocrine 40, 96, 164exocrine 40, 96, 97glandular system 40,

41lymphatic system 96,

97glucagon 96glucose 45, 54–57, 63,

109, 193gluten 46glycerols 63–64, 77glycogen 45goiter 113golfer’s elbow 72, 188gonorrhea 21goose bumps 106gout 147, 161growing pains 100growth 40, 98–100, 164growth hormone 96, 99,

100gums 176

Hhair 37, 164–165, 180,

181halitosis 67hammertoe 147, 161hamstring injuries 101handicaps 69hay fever 143headaches 10, 12, 46health food 102

heart 27, 36, 37, 50,103–104, 118, 169

blood pressure 35cardiac muscles

137–138heart attack 12, 35, 48, 105,

145, 192heartbeat 26, 35, 68, 141heartburn 66, 112heart disease 18, 73, 81, 85,

102, 118, 124, 173heat exhaustion 106, 194heat sickness 106heatstroke 106, 195height loss 8hematoma 33, 42hemoglobin 13–14, 114,

168hemophilia 185hemorrhage 192hemorrhoids 52–53, 67heparin 39hernia 68, 107

femoral 107hiatal 107incarcerated 107inguinal 107strangulated 107umbilical 107

herpes 34high blood pressure see

hypertensionhigh-density lipoproteins

(HDLs) 85hip 38, 108, 123, 126

replacement 121–122,122

histamine 23, 39homeostasis 109hookworm 13hormones 40, 77, 96–97,

99, 100, 109, 137, 163,164

house dust mite 24, 24housemaid’s knee 119humerus 29, 72, 72, 130,

177hunger 109hydrochloric acid 63hydrocortisone 24hydrotherapy 160hygiene 92, 172hyperactivity 11, 124hyperkalemic paralysis

140hypertension 10, 35, 51, 62,

73, 75, 145, 173hyperventilation 110hypoglycemia 55, 76, 193hypokalemic paralysis 140hypothalamus 96, 164hypothermia 128

Iibuprofen 12ice therapy 111iliac 29, 108, 108immune deficiency 131immune system 37–38,

73, 202indigestion 66, 112inflammation 12

arthritis 20–22influenza 198

ingrown toenails 79insomnia 51, 73insulin 45, 55–57, 96, 193intestines 63–65

hernias 107, 107large 40, 40, 64, 65small 40, 40, 46, 46,

63–64, 64, 65, 97, 107intrinsic factor 13–14iodine 58, 113, 135, 144iron 13, 58, 87–88, 114, 135,

144irritable bowel syndrome

68, 115–116ischium 29isometric exercise 117, 157

Jjogging 118, 156joints 37, 38, 123, 130

Alexander technique 10ankle 38, 111, 126, 189arthritis 20–22dislocation 93–95, 119disorders 119–120double-jointedness 119elbow 72, 120, 123, 130hip 108, 123, 126knee 28, 38, 119, 120, 123,

125, 126, 127, 147, 189loose bodies 125orthopedics 146–147physical therapy 160posture 162replacement 22, 108,

108, 121–122revision 121shoulder 28–29, 72, 119,

123, 147, 177spinal 119, 123sprains 111, 119, 130, 191

jugular vein 50junk food 124

Kkeratin 180keratoses, solar 194kidneys 36, 40kidney stones 43knee 28, 38, 119, 120, 123,

125, 126, 127, 147, 189osteoarthritic 21replacement 121–122,

122water on 119

kwashiorkor 131kyphosis 175

Llacteals 64larynx 168laxatives 53, 66lead poisoning 71leg 126–127lethargy 128–129, 198life expectancy 9ligaments 36, 37, 123, 130,

146, 178, 191lipase 63lipoproteins 77, 81, 85lips 111liver 27, 36, 40, 63, 65Lou Gehrig’s disease 140,

184

low-density lipoproteins(LDLs) 81, 85

lumbago 29, 47lumbar region 28, 29, 183lungs 26, 36, 37, 38–39, 39,

50, 103, 118, 168, 169lymphatic system 96, 97lymph nodes 96, 97, 97lymphocytes 96, 97

Mmacrobiotics 58, 199magnesium 58, 135malabsorption 67malnutrition 131–132mammary glands 40, 97,

97, 195manganese 135marasmus 131massage 133, 160, 171, 191masturbation 165measles 198meditation 171melanin 180, 194melanoma 181melatonin 97meningitis 184menopause 43, 81menstruation 13, 16, 81,

114, 129, 143, 164meperidine 152meridians 5metabolic rate 60metabolism 18, 73, 74, 96,

118basal 32, 58

metatarsals 78, 78, 147migraines 12, 173milk 40, 63, 96, 97, 134minerals 43, 58, 82, 83,

85–88, 113, 114, 135, 144moles 180–181mononucleosis, infectious

96, 198monosodium glutamate

82, 83morphine 12, 152motivational syndrome

129motor neuron disease

136, 140, 184mouth 38, 39, 40, 40, 63,

65ulcers 66

mucus 63multiple sclerosis (MS)

153, 184muscles 38, 137–138, 141,

146, 163, 178, 196aerobic exercise 7, 118aging 8cardiac 137–138cramps 54, 139–140diseases and disorders

139–140, 188–189isometric exercise 117massage 133, 160skeletal (voluntary) 37,

137smooth (involuntary)

37, 137strained 139, 140, 191tissue 36, 36, 37

muscular dystrophy 140

Index


208

myelin 141myelitis 153myositis 139–140myxedema 113, 128

Nnausea 67negative feedback 109nervous system 36,

40–41, 110, 141–142,150, 184

autonomic 26–27central 40–41, 41nerve cells 37parasympathetic

26–27, 27sympathetic 26, 27

neuralgia 10neurons 136, 141neurotransmitters 26, 141noninsulin-dependent

diabetes (NIDD) 56nonsteroidal anti-

inflammatory drugs(NSAIDs) 12, 12

noradrenaline 77, 96norepinephrine 26nose 38, 168nosebleed 143nutrition 84–90

malnutrition 131–132nutritional diseases

144see also diet; food

Oobesity 19, 56, 58, 59, 73,

75, 85, 112, 121, 145weight control 60–62,

204onychogryphosis 161organelles 36organic foods 102organs 36orthopedics 146–147ossification 178osteoarthritis 10, 20, 21osteopathy 29, 148osteoporosis 29, 43, 147ovaries 41, 41, 96, 97, 164ovum 41oxygen 13, 37, 38–39, 50,

73, 103, 114, 149,168–169

aerobic exercise 7

Ppain 150–152

acupressure 5acupuncture 6, 150, 152analgesics 12endorphins 5phantom limb 141, 152referred 152

pancreas 41, 45, 63, 65, 96,97, 97

panic attack 110paralysis 153, 192

hyperkalemic 140hypokalemic 140

paraplegia 153parasites 13, 128parasympathetic nervous

system 26

parathyroid glands 43, 96,97

paratyphoid 92patella 125, 125, 126, 127peak flow meter 24pectoral girdle 28–29pellagra 202pelvic girdle 29, 108, 108pepsin 63periorbital hematoma 33peripheral nervous system

141peristalsis 52, 64, 115peritonitis 67perspiration see sweatpharynx 168phosphorus (phosphate)

43, 58, 96, 135, 203photosynthesis 45physical examination 154physical fitness 155–159physical therapy 160pigeon toes 78Pilates 117, 162piles see hemorrhoidspinched nerve 141, 160pineal gland 97, 97pituitary gland 40, 41, 77,

96, 97, 100, 164placenta 40plantar warts 79, 161pneumonia 149podiatry 161poisoning, food 92poliomyelitis 153, 184pollution 18, 23polymyalgia rheumatica

140polyphenols 81polyps 67polyunsaturates 77, 89post-traumatic stress

syndrome 129posture 28, 130, 162

Alexander technique10, 162

potassium 58, 135, 173pregnancy 19, 54, 114, 129,

180prolactin 96prostaglandins 12, 12prosthesis 121–122, 121proteins 39, 44, 45, 58,

60–61, 63, 85–86, 88,102, 131, 134, 163

psoriasis 21psychoneuroimmunology

36ptyalin 63puberty 99, 164–166pulmonary circulation 103pulmonary embolism 122pulse 35Putti-Platt operation 119

Rradius 72, 72, 130rectum 40, 64, 65reflexes 167, 184relaxation 133, 170–171,

205repetitive stress 121reproductive systems 40,

41

respiration 39respiratory system 38–39,

39, 168–169rest 170–171Reye’s syndrome 12rheumatic fever 21rheumatism 120rheumatoid arthritis 20,

120, 121, 126, 174ribs 120, 168, 178–179rickets 144, 153, 203ringworm 25Ritalin 11

Ssaccule 30, 31sacrum 28–29, 29, 183saliva 63, 65salivary glands 40, 41, 65,

97, 97salmonella 66, 92, 172salt 96, 173scapula 29, 72, 177schizophrenia 129sciatica 47, 126, 174sciatic nerve 126, 174scoliosis 175scurvy 144, 176, 201sebaceous glands 97, 180,

181sebum 97semen 164, 165semicircular canals 30, 31senses 41septicemia 128sex hormones 96, 99shock 103shoes 28, 34, 78–80shoulder 28–29, 72, 119,

123, 147, 177sinews see tendonssinusitis 24, 143skeletal system 36, 37, 38,

178–179see also bones;

cartilage; ligaments;muscles

skin 36, 37–38, 37, 180–181aging 8, 180blisters 34bruises 33, 42cancer 181color 180fungal infections 25, 79sunburn 34, 194wrinkles 5, 8, 133, 180,

194skull 123, 178–179sleep 129, 157, 170slipped disk 29, 29, 47, 119,

174, 182smoking 18, 48, 52, 66,

105, 112, 168, 192aging process 8

sodium chloride 135, 144,173

somatic nervous system141, 142

sperm 41, 164spinal column 28–29, 29,

123, 178–179, 183, 184aging 8chiropractic 47joint injuries 119

scoliosis 175see also slipped disk

spinal cord 27, 40–41, 41,141, 142, 178, 184

paraplegia 153sports 185–187

injuries 188–190, 197sprains and strains 101,

111, 119, 130, 139–140,191

staphylococcal poisoning66, 92

starvation 131sternum 178–179steroids 23–24Still’s disease 20–21stomach 36, 39–40, 40,

63, 65, 66strains see sprains and

strainsstress-related disorders

10, 66, 68, 155asthma 23backache 29fainting 76hyperventilation 110irritable bowel

syndrome 68, 115–116stroke 12, 35, 48, 153, 173,

192sugars 45, 63, 124, 193sunburn 34, 194sunlight 18, 200sunstroke 106sutures 123sweat 27, 37, 71, 96–97,

106, 106, 109, 139, 180,181, 195

sympathetic nervoussystem 26

synovial fluid 120, 123, 125systemic circulation 103systolic pressure 35, 35

Ttannin 51tapeworm 13tea 51, 81tear ducts 40tear glands 97teeth 43, 131, 134, 176, 202,

203tendonitis 72, 196 tendons 36, 126, 146,

188–189, 196, 197tennis elbow 72, 197testes 41, 41, 96, 97, 164testosterone 164thalamus 151thalassemia 14theophylline 51thermoregulation 106,

109, 195thoracic vertebrae 29,

183throat 63thrombosis 192thymus 97thyroid gland 40, 41, 77,

96, 97, 100, 113,128–129, 145

thyroxine 99, 100, 113,128–129, 198

tibia 123, 125, 125, 126, 127

tiredness 10, 14, 27, 198chronic fatigue

syndrome 49lethargy 128–129, 198

tissues 36, 36, 163toxins 92trachea 23, 38, 39, 39, 168,

169transcutaneous electrical

nerve stimulation(TENS) 152

triceps 72trypsin 63–64tuberculosis 21tumors 27, 67, 84tympanic membrane 30typhoid fever 66, 128typhus 128

Uulcers 13, 20, 66ulna 72, 72, 130ulnar nerve 36, 72ultrasound 160ultraviolet radiation 18,

194ureters 40urethra 40urinary system 40urine 40, 71uterus 41, 41utricle 30, 31

Vvaricose veins 126, 161vegetarianism 58, 84, 199veins 37, 50, 50, 103

hemorrhoids 52–53varicose 126, 161

venules 50vertebrae 28–29, 28, 178,

182see also spinal column

villi 40, 46, 46, 64, 64vitamins 58, 82, 83, 85–89,

132, 200–203A 87–88, 144, 200–201B 13–14, 51, 88, 102, 144,

200–202C 18, 82, 87, 144, 176,

200–202D 43, 140, 144, 200–203E 18, 82, 102, 200–203K 200–201, 203

vomiting 66, 67, 71, 92

Wwaste products 37, 38, 40,

50, 168–169water 71, 85–86water on knee 119weight control 15–17,

60–62, 73, 75, 86, 204whiplash 191whole foods 102windpipe see tracheawrinkles 5, 8, 133, 180, 194writer’s cramp 54

Yyoga 74, 162, 171, 205

Zzinc 58, 135

Index


2011 nutrition and fitness

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